"a- -ing" meaning in Anglais

{
  "categories": [
    {
      "kind": "other",
      "name": "Circonfixes en anglais",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Anglais",
      "orig": "anglais",
      "parents": [],
      "source": "w"
    }
  ],
  "etymology_texts": [
    "Du vieil anglais an, qui est devenu la préposition on et du suffixe -ing."
  ],
  "lang": "Anglais",
  "lang_code": "en",
  "notes": [
    "On écrit souvent un trait d’union après a."
  ],
  "pos": "circumfix",
  "pos_title": "Circonfixe",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Termes archaïques en anglais",
          "parents": [],
          "source": "w"
        }
      ],
      "examples": [
        {
          "text": "Gather ye rosebuds while ye may,\nOld time is still a-flying:\nAnd this same flower that smiles to-day\nTo-morrow will be dying.\nThe glorious lamp of heaven, the sun,\nThe higher he’s a-getting, … — (Robert Herrick, To the Virgins, to Make Much of Time, 1648)"
        }
      ],
      "glosses": [
        "Circonfixe pour former le participe présent d’un verbe."
      ],
      "id": "fr-a-_-ing-en-circumfix-g2fxD6ye",
      "tags": [
        "archaic"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "\\ə ɪŋ\\"
    }
  ],
  "tags": [
    "morpheme"
  ],
  "word": "a- -ing"
}

{
  "categories": [
    "Circonfixes en anglais",
    "anglais"
  ],
  "etymology_texts": [
    "Du vieil anglais an, qui est devenu la préposition on et du suffixe -ing."
  ],
  "lang": "Anglais",
  "lang_code": "en",
  "notes": [
    "On écrit souvent un trait d’union après a."
  ],
  "pos": "circumfix",
  "pos_title": "Circonfixe",
  "senses": [
    {
      "categories": [
        "Termes archaïques en anglais"
      ],
      "examples": [
        {
          "text": "Gather ye rosebuds while ye may,\nOld time is still a-flying:\nAnd this same flower that smiles to-day\nTo-morrow will be dying.\nThe glorious lamp of heaven, the sun,\nThe higher he’s a-getting, … — (Robert Herrick, To the Virgins, to Make Much of Time, 1648)"
        }
      ],
      "glosses": [
        "Circonfixe pour former le participe présent d’un verbe."
      ],
      "tags": [
        "archaic"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "\\ə ɪŋ\\"
    }
  ],
  "tags": [
    "morpheme"
  ],
  "word": "a- -ing"
}