a-

a- + trist (“sad”) → athrist (“very sad, sorrowful”)

a- + traidd (“piercing, penetration”) → athraidd (“permeable”)

affirmative prefix, emphasises prefixed word


h

ei hiaith

i’n heglwys

un ar hugain


bio-

bio- + amrywiaeth (“variety, diversity”) → bioamrywiaeth (“biodiversity”)

bio- + cemeg (“chemistry”) → biocemeg (“biochemistry”)

bio- + diraddio (“to degrade”) → bioddiraddio (“to biodegrade”)

bio- + -leg (“-logy”) → bioleg (“biology”)


an-

From Middle Welsh an-, from Proto-Brythonic *an-, from Proto-Celtic *an-, from Proto-Indo-European *n̥-. Cognate with Cornish an-.

an- + parch (“respect”) → amarch (“disrespect”)

an- + prisiadwy (“valuable”) → amhrisiadwy (“invaluable”)

an- + teg (“fair”) → annheg (“unfair”)

an- + cofio (“to remember”) → anghofio (“to forget”)

an- + diwedd (“end”) → anniwedd (“endless”)

an- + gwybod (“to know”) → anwybod (“ignorance”)

an- + mantais (“advantage”) → anfantais (“disadvantage”)

af-

used before ''gl'', ''ll'', ''rh'', and consonantal ''i''

not, un-, non-, an-, dis-, negative prefix


an-

From Proto-Celtic *ande-, *ando- (“inside”).


di-

Proto-Celtic *dī- (“from, of”), from Proto-Indo-European *de. Cognate with Cornish di-.

di- + goddef → dioddef

di- + golwch → diolch

di- + enw (“name”) → dienw (“anonymous”)

di- + paid (“pause, respite”) → di-baid (“ceaseless, incessant”)

di- + swydd (“job, office”) + -o → diswyddo (“dismiss, discharge, sack, make redundant”)

without, -less, de-, a-, negative prefix


dis-

dis- + taw (“quiet, silent”) → distaw (“silent, noiseless”)

dis- + pwyll (“consideration”) → disbwyll (“discretion, prudence”)

dis- + cloff (“lame”) → disgloff (“sure footed, agile”)


en-

en- + mawr (“big”) → enfawr (“huge”)

en- + pyd (“danger”) → enbyd (“dangerous, exceeding, pressing”)


e-

From English e-, an abbreviation of electronic.

e- + llyfr (“book”) → e-lyfr (“e-book”)

e- + masnach (“trade, commerce”) → e-fasnach (“e-commerce”)

e- + post (“post, mail”) → e-bost (“email”)

e- + dysgu (“to learn”) → e-ddysgu (“e-learning”)


ad-

From Proto-Brythonic *ate-, from Proto-Celtic *ati-. from Proto-Indo-European *éti. Cognate with Cornish as-, English ed-, Latin et (“and”), Sanskrit अति (ati, “over-”).

ad- + llais (“voice”) → adlais (“echo”)

ad- + talu (“to pay”) → ad-dalu (“to refund”)

ad- + blas (“taste”) → adflas (“aftertaste”)

ad- + cas (“hated, nasty”) → atgas (“hateful, detestable”)


er-

er- + glynu (“to attach”) → erlyn (“to pursue, prosecute”)


arch-

From Latin archi- or English arch-. Cognate with Cornish argh-.

arch- + angel (“angel”) → archangel (“archangel”)

arch- + marchnad (“market”) → archfarchnad (“supermarket”)

arch- + esgobaeth (“bishopric”) → archesgobaeth (“archbishopric, primacy”)


para-

See English para-, from Ancient Greek παρα- (para-).

para- + meddyg (“doctor”) → parafeddyg (“paramedic”)

para- + normal (“normal”) → paranormal (“paranormal”)

para- + ymatebol (“responsive, reactive”) → paraymatebol (“parasympathetic”)


nitro-

(organic chemistry) nitro- (containing nitrogen)


bromo-

(organic chemistry) bromo- (containing bromine)


nitr-

(organic chemistry) alternative form of nitro- (“containing nitrogen”), used before a vowel


is-

is- + arlywydd (“president”) → is-arlywydd (“vice-president”)

is- + deddf (“law”) → is-ddeddf (“byelaw”)

is- + rhywogaeth (“species”) → isrywogaeth (“subspecies”)

is- + teitl (“title”) → isteitl (“subtitle”)

lower, deputy, lieutenant, sub-, vice-, under-, by-


brom-

(organic chemistry) Alternative form of bromo- (“containing bromine”), used before a vowel


cloro-

From Ancient Greek χλωρός (khlōrós, “pale green”).

uder

(organic chemistry) chloro- (chlorine, green)


dar-

From Proto-Celtic *do-are-, corresponding to dy- (“to, together”) + ar- (“on; near”).

dar- + llith (“reading”) → darlith (“lecture”)

dar- + lledu (“to spread, to broaden”) → darlledu (“to broadcast”)

dar- + cludo (“to carry, to transport”) → dargludo (“to conduct (electricity)”)


llys-

Perhaps from the same root as lled (“part, partially”) and lled- (“part, partially”) or possibly lled (“challenge to a witness”). Cognate with Cornish les-.

llys- + merch (“daughter”) → llysferch (“stepdaughter”)

llys- + tad (“father”) → llystad (“stepfather, stepdad”)

llys- + enw (“name”) → llysenw (“nickname”)

llys- + perl (“pearl”) → llysberl (“false pearl”)


all-

From Proto-Celtic *alyos, from Proto-Indo-European *h₂élyos. Cognate with Old English el-, Ancient Greek ἄλλος (állos).

all- + morio (“to travel by sea”) → allforio (“to export”)

all- + plyg (“folded”) → allblyg (“extrovert”)

all- + pwn (“load, burden”) → allbwn (“output”)

all- + tud (“people, nation”) → alltud (“stranger; exile”)

all- + ffôn (“phone”) → allffon (“allophone”)


ap

From fab, soft mutation of mab (“son”). Cognate with Breton prefix ab- and more distantly Irish and Scottish Gaelic mac.


af-

From Proto-Brythonic *aβ̃-, from Proto-Celtic *am-, allophonic variant of *an- before *b and *ɸ.

af- + glân (“clean; honest”) → aflan (“corrupt, evil”)

af- + llwyddiannus (“successful”) → aflwyddiannus (“unsuccessful”)

af- + rhwydd (“easy”) → afrwydd (“difficult”)

af- + iechyd (“health”) → afiechyd (“sickness, illness”)


dam-

Proto-Celtic *do-ambi-, from *do- + *ambi-, equivalent to dy- (“to, together”) + am- (“around”).

dam- + cylchu (“to circle, to surround”) → damgylchu (“to encompass, to surround”)

dam- + amcanu (“to estimate”) → damcanu (“to conjecture, to speculate”)


ar-

From Proto-Brythonic *ar-, from Proto-Celtic *ɸare.

ar- + nofio (“to swim”) → arnofio (“to float”)

ar- + ysgrif (“writing”) → arysgrif (“inscription, epigraph”)

ar- + lliw (“colour”) → arlliw (“shade”)

ar- + môr (“sea”) → arfor (“coast”)


es-

es- + plygu (“fold”) → esblygu (“evolve”)


cyt-

cyt- + pwys (“pound, weight”) → cytbwys (“balanced”)

cyt- + cân (“song”) → cytgan (“chorus”)

cyt- + tras (“strain, pedigree”) → cytras (“akin, cognate”)


tra-

tra- + dwy (“two”) → tradwy (“in three days time”)

tra- + môr (“sea”) → tramor (“abroad”)

tra- + plith (“middle, midst”) → traphlith (“topsy-turvy, in confusion”)

tra- + pont (“bridge”) → traphont (“viaduct”)

tra- + chwant (“desire, lust”) → trachwant (“covetousness, greed”)

tra- + ffordd (“road”) → traffordd (“motorway”)


at-

at- + hebu (“to speak, to say”) → ateb (“to answer”)

at- + tyfu (“to grow”) → atyfu (“to germinate”)

at- + ffurfio (“to form”) → atffurfio (“to reform, to regenerate”)

at- + cas (“hated, nasty”) → atgas (“hateful, detestable”)


ym-

Ultimately from Proto-Indo-European *h₂m̥bʰi (“round about, around”). Cognate with Cornish om-, Latin amb- (“around, about”), ambi- (“both”), English um-, umb- (“around, about”), Ancient Greek ἀμφί (amphí, “around, about”).

cog

ym- + golchi (“wash”) → ymolchi (“wash oneself, have a wash”)

ym- + uno (“to unite”) → ymuno (“to join”)

ym- + diswyddo (“dismiss, discharge”) → ymddiswyddo (“resign”)

ym- + gweld (“to see”) → ymweld (“to visit”)

ym- + lladd (“to kill”) → ymladd (“to fight”)

ym- + holi (“ask”) → ymholi (“to inquire”)


gor-

From Proto-Brythonic *gwor-, from Proto-Celtic *uɸor-, from Proto-Indo-European *upér. Cognate with Cornish gor-, Breton gour- and English over-.

gor- + tew (“fat”) → gordew (“obese”)

gor- + actif (“active”) → goractif (“hyperactive”)

gor- + cyffwrdd (“to touch”) → gorgyffwrdd (“to overlap”)

gor- + gyrru (“to drive”) → goryrru (“to speed”)


cy-

Probably related to cyf-. Cognate with Cornish ke- and Cornish ky-.

cy- + syniad (“idea”) → cysyniad (“concept”)

cy- + ffordd (“road, way”) → cyffordd (“junction”)

cy- + gwaith (“work”) → cywaith (“joint work, joint operation”)

cy- + gwir (“true, real”) → cywir (“correct”)

cy- + drwg (“bad”) → cynddrwg (“as bad”)

cy- + hyd (“length”) → cyhyd (“as long”)

cy- + maint (“size, amount”) → cymaint (“as big, as much”)


am-

am- + llen (“sheet”) → amlen (“envelope”)

am- + ysgrifio (“to write, to inscribe”) → amsgrifio (“to circumscribe”)

am- + cau (“to close”) → amgáu (“to enclose”)


dat-

dat- + plygu (“to fold”) → datblygu (“to unfold, to develop”)

dat- + cuddio (“to hide”) → datguddio (“to reveal”)

dat- + drysu (“to entangle, to confuse”) → datrys (“to disentangle, to solve”)

dat- + canu (“to sign”) → datgan (“to announce, to declare”)


eil-

eil- + gradd (“degree, grade”) → eilradd (“secondary, second-rate”)

eil- + cylch (“circle, cycle”) → eilgylch (“recycled”)

eil- + twym (“warm”) → eildwym (“reheated”)


ail-

ail- + creu (“to create”) → ail-greu (“to recreate”)

ail- + cylchu (“to circle”) → ailgylchu (“to recycle”)

ail- + gwerthusiad (“appraisal”) → ailwerthusiad (“reappraisal”)


go-

From Proto-Celtic *uɸo-, ultimately from Proto-Indo-European *upo. Cognate with Cornish go-, Old Irish fo, Scottish Gaelic fo.

go- + llosg (“burning”) → golosg (“charcoal”)

go- + pen (“head”) + -ydd → gobennydd (“pillow”)

go- + tŷ (“house”) → gody (“outhouse”)


dy-

From Middle Welsh dy-, from Proto-Celtic *dus-, from Proto-Indo-European *dus-.

dy- + llaw (“hand”) → dylaw (“clumsy”)


dy-

From Proto-Celtic *do-, from Proto-Indo-European *do.

dy- + mynnu (“to insist”) → dyfyn (“summons”)

dy- + crŷn (“trembling”) → dychryn (“to frighten”)


dad-

From Proto-Celtic *do-ate-, equivalent to dy- + ad-. Cognate with Cornish das-.

dad- + pacio (“to pack”) → dadbacio (“to unpack”)

dad- + gwneud (“to do”) → dad-wneud (“to undo”)

dad- + llwytho (“to load”) → dadlwytho (“to unload”)

dad- + ennill (“to win, to earn”) → dadennill (“to regain”)


cyn-

From Proto-Brythonic *kɨnt (“former, previous”). Cognate with Cornish kyn- and Cornish kyns-.

inh

cyn- + gŵr (“husband”) → cyn-ŵr (“ex-husband”)

cyn- + aelod (“member”) → cyn-aelod (“former member”)


cyn-

From Proto-Brythonic *köβ̃-. Cognate with Cornish ken-.

cyn- + twrf (“loud noise”) → cynnwrf (“commotion, excitement”)


hy-

From Middle Welsh hy-, from Old Welsh hi-, from Proto-Brythonic *hu-, from Proto-Celtic *su-, from Proto-Indo-European *h₁su- (“good”). Cognate with Cornish he- and Ancient Greek εὐ- (eu-, “good”).

hy- + rhwydd (“easy”) → hyrwydd (“very easy”)

hy- + glân (“clean”) → hylan (“hygienic”)

hy- + plyg (“folded”) → hyblyg (“flexible”)

hy- + byw (“alive”) → hyfyw (“viable”)

added to verbal roots, indicates 'easy to X', 'X-able'


cyd-

cyd- + perchennog (“owner”) → cyd-berchennog (“co-owner”)

cyd- + dibynnol (“dependent”) → cyd-ddibynnol (“co-dependent, interdependent”)

cyd- + glynu (“to stick, to adhere”) → cydlynu (“to cohere, to coordinate”)


cyf-

From Middle Welsh kyu-, from Old Welsh com-, from Proto-Brythonic *köβ̃-, from Proto-Celtic *kom-. Cognate with Cornish kev-.

cyf- + un (“one”) → cyfun (“concordant, united”)

cyf- + amod (“condition”) → cyfamod (“covenant”)

cyf- + enw (“name”) → cyfenw (“surname”)

cyf- + lliw (“colour”) → cyfliw (“of the same colour”)

cyf- + oed (“age, time”) → cyfoed (“contemporary, of the same age, at the same time”)

cyf- + uwch (“higher”) → cyfuwch (“as high”)

cyf- + llym (“sharp, keen”) → cyflym (“quick, fast”)

cyf- + agos (“near”) → cyfagos (“neighbouring, adjacent”)

cyf- + llawn (“full”) → cyflawn (“complete, total”)


ech-

From Proto-Celtic *exs-, from Proto-Indo-European *h₁eǵʰs (“out of”). Cognate with Old Irish ess- (see Irish as), Latin ex-, Ancient Greek ἐκ- (ek-).
Originally es- was the form before plosives and ech- before vowels, but the latter has spread by analogy.

ech- + plyg (“folded”) → echblyg (“explicit”)

ech- + torri (“to cut, to break”) → echdorri (“to erupt”)

ech- + tynnu (“to pull, to draw”) → echdynnu (“to extract”)

ech- + doe (“yesterday”) → echdoe (“day before yesterday”)

ech- + nos (“night”) → echnos (“night before last”)


gwrth-

From Proto-Celtic *writ-. Cognate with Welsh wrth, Cornish gorth-, Irish frith-, Scottish Gaelic ri and Latin versus (“against”).

gwrth- + taro (“to hit, to strike”) → gwrthdaro (“to clash, to collide”)

gwrth- + tystio (“to witness”) → gwrthdystio (“to protest”)

gwrth- + plaid (“(political) party”) → gwrthblaid (“opposition party”)

gwrth- + llwydni (“mildew”) → gwrthlwydni (“mildew resistant”)

gwrth- + biotig (“biotic”) → gwrthfiotig (“antibiotic”)

gwrth- + ystyr (“meaning”) → gwrthystyr (“antonym”)


mewn-

mewn- + morio (“to travel by sea”) → mewnforio (“to import”)

mewn- + plyg (“folded”) → mewnblyg (“introvert”)

mewn- + pwn (“load, burden”) → mewnbwn (“input”)


rhag-

See rhag. Cognate with Cornish rag- and Cornish rak-.

rhag- + llen (“sheet”) → rhaglen (“programme”)

rhag- + golwg (“view, sight”) → rhagolwg (“preview”)

rhag- + gweld (“to see”) → rhag-weld (“to foresee”)


rhyng-

rhyng- + gweithio (“to work”) → rhyngweithio (“to interact”)

rhyng- + rhwyd (“net”) → rhyngrwyd (“internet”)

rhyng- + personol (“personal”) → rhyngbersonol (“interpersonal”)


tan-

tan- + môr (“sea”) → tanfor (“undersea, submarine”)

tan- + gwariant (“spending”) → tanwariant (“underspending”)

tan- + ysgrifio (“to write, to inscribe”) → tanysgrifio (“to subscribe”)


traws-

Cognate with Breton treuz- and Cornish treus-. See traws.

traws- + plannu (“to plant”) → trawsblannu (“to transplant”)

traws- + torri (“to cut”) → trawstorri (“to cross-cut”)

traws- + acen (“accent”) → trawsacen (“syncopation”)


tros-

tros- + lleisio (“to voice”) → trosleisio (“to voiceover, to dub”)

tros- + gwydryn (“glass”) → troswydryn (“overglaze”)

tros- + ffordd (“road”) → trosffordd (“flyover”)


can-

From Proto-Brythonic *kanta-, from Proto-Indo-European *ḱm̥-teh₂, from *ḱóm. Related to gan (“with”) and cognate with Ancient Greek κατά (katá, “against; downwards”).

cog

can- + llaw (“hand”) → canllaw (“rail, guide”)

can- + glynu (“to adhere, to stick”) → canlyn (“to follow, to pursure”)

can- + dal (“to hold, to catch”) → cynnal (“to hold, to maintain”)


add-

From Proto-Brythonic *ad-, from Proto-Celtic *ad-, from Proto-Indo-European *h₂éd (“near, at”). Cognates include Latin ad and English at.

add- + mwyn (“mild”) → addfwyn (“gentle, meek”)

add- + oer (“cold”) → addoer (“very cold, chilly”)


cyfr-

cyfr- + trist (“sad”) → cyfrdrist (“extremely sad, grievous”)

cyfr- + coll (“loss”) → cyfrgoll (“total loss, damnation”)

cyfr- + gwŷs → cyfrwys (“cunning, crafty”)


traf-

traf- + llyncu (“to swallow”) → traflyncu (“to gobble, to swallow up”)


try-

try- + gloyw (“bright, shining”) → tryloyw (“transparent”)

try- + mesur (“measure, measurement”) → tryfesur (“diameter”)

try- + gwanu (“to stab”) → trywanu (“to stab, to pierce”)

try- + llwyr (“entire”) → trylwyr (“thorough”)

try- + tân (“fire”) → trydan (“electricity”)

try- + rhyw (“kind, sort”) → tryryw (“thoroughbred”)


try-

try- + gwŷr (“men”) → trywyr (“three men”)

try- + cant (“hundredd”) → trycant (“three hundred”)

try- + bêr (“spear, skewer”) → tryfer (“trident”)


aml-

aml- + llawr (“floor, storey”) → aml-lawr (“multistorey”)

aml- + dewis (“choice”) → amlddewis (“multiple choice”)

aml- + cellog (“cellular”) → amlgellog (“multicellular”)


dym-

Proto-Celtic *do-ambi-, from *do- + *ambi-, equivalent to dy- (“to, together”) + am- (“around”).

dym- + chwêl (“turn”) → dymchwel (“to overturn, to overthrow, to demolish”)

dym- + uno (“to wish, to desire”) → dymuno (“to wish”)


lled-

lled- + rhith (“illusion; phantom”) → lledrith (“magic; apparition”)

lled- + gorwedd (“to lie (down)”) → lled-orwedd (“to recline”)

lled- + dargludydd (“conductor”) → lled-ddargludydd (“semiconductor”)


cam-

From cam (“crooked; incorrect; unjust”).

cam- + gosod (“to place”) → camosod (“to misplace”)

cam- + trin (“to treat, handle”) → cam-drin (“to mistreat, abuse”)

cam- + syniad (“idea, concept”) → camsyniad (“error, mistake, misconception”)


pedr-

pedr- + ongl (“angle”) → pedrongl (“quadrilateral, square”)

pedr- + rhannu (“to divide, to share”) → pedrannu (“to quarter”)

pedr- + sill (“syllale”) → pedrsill (“tetrasyllabic”)


pedry-

From Middle Welsh pedry-, from Proto-Celtic *kʷetru-, from Proto-Indo-European *kʷetwr̥-.
Related to pedair (“four”).

pedry- + ban (“corner”) → pedryban (“four corners; tetrastich”)

pedry- + dydd (“day”) → pedrydydd (“fourth day; quartan”)

pedry- + llaw (“hand”) → pedrylaw (“dextrous, adroit”)

pedry- + llef (“shout, cry”) → pedrylef (“eloquent, sonorous”)


prif-

From prif, from Latin prīmus. Compare Irish príomh-, English prime.


hunan-

hunan- + eglur (“clear”) → hunaneglur (“self-evident”)

hunan- + lladdiad (“killing”) → hunanladdiad (“suicide”)

hunan- + parch (“respect”) → hunan-barch (“self-respect”)

hunan- + ynysu (“to isolate”) → hunanynysu (“to self-isolate”)


uwch-

From the comparative adjective uwch (“higher”).

over-, hyper-, meta-, super, supra-, top-, ultra-


uch-

Alternative form of uwch- (“super-, hyper-”)


deu-

From Middle Welsh deu, from Old Welsh dou, from Proto-Brythonic *dọw, from Proto-Celtic *duwo, from Proto-Indo-European *dwóh₁. Corresponds to dau m (“two”).

deu- + llawr (“floor”) → deulawr (“two-storey”)

deu- + pegwn (“pole”) → deubegwn (“bipolar”)

deu- + rhyw (“sex”) → deuryw (“bisexual, hermaphrodite”)


dwy-

From Proto-Celtic *dwī (feminine of *duwo), from Proto-Indo-European *dw-ih₂, feminine of *dwóh₁. Corresponds to dwy f (“two”).

dwy- + gwaith (“time”) → dwywaith (“twice”)

dwy- + awr (“hour”) → dwyawr (“(a period of) two hours”)

dwy- + ffordd (“way”) → dwyffordd (“reversible”)

dwy- + iaith (“language”) + -og → dwyieithog (“bilingual”)

dwy- + llaw (“hand”) → dwylo (“hands”)


clor-

(organic chemistry) Alternative form of cloro- (“containing chlorine”), used before a vowel


fflworo-

(organic chemistry) fluoro- (containing fluorine)


fflwor-

(organic chemistry) Alternative form of fflworo- (“containing fluorine”), used before a vowel


ffeno-

(organic chemistry) pheno- (containing phenol)


sylff-

(organic chemistry) Alternative form of sylffo- (“containing sulfur”), used before a vowel


sylffo-

(organic chemistry) sulfo- (containing sulfur)


morffo-

Adapted from English morpho-, representing a combining form of Ancient Greek μορφή (morphḗ, “form”).

pertaining to shape, form, or morphology.


dir-

dir- + crynu (“to tremble”) → dirgrynu (“to quake”)

dir- + llawn (“full”) → dirlawn (“saturated”)