"-isti" meaning in Latin

{
  "etymology_text": "From a probable Proto-Italic -istai, likely formed from merging the Proto-Indo-European second person singular aorist ending th₂e with an aorist stem -s-.",
  "head_templates": [
    {
      "args": {
        "1": "la",
        "2": "suffix"
      },
      "expansion": "-isti",
      "name": "head"
    }
  ],
  "lang": "Latin",
  "lang_code": "la",
  "pos": "suffix",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Latin entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with 4 entries",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        }
      ],
      "derived": [
        {
          "word": "-āvistī"
        },
        {
          "word": "-uistī"
        },
        {
          "word": "-īvistī"
        }
      ],
      "glosses": [
        "Used for the second person present perfect singular form of any regular verb."
      ],
      "id": "en--isti-la-suffix-MnHFhhpZ",
      "links": [
        [
          "second person",
          "second person#English"
        ],
        [
          "present perfect",
          "present perfect#English"
        ],
        [
          "singular",
          "singular#English"
        ]
      ],
      "tags": [
        "morpheme"
      ]
    }
  ],
  "word": "-isti"
}

{
  "derived": [
    {
      "word": "-āvistī"
    },
    {
      "word": "-uistī"
    },
    {
      "word": "-īvistī"
    }
  ],
  "etymology_text": "From a probable Proto-Italic -istai, likely formed from merging the Proto-Indo-European second person singular aorist ending th₂e with an aorist stem -s-.",
  "head_templates": [
    {
      "args": {
        "1": "la",
        "2": "suffix"
      },
      "expansion": "-isti",
      "name": "head"
    }
  ],
  "lang": "Latin",
  "lang_code": "la",
  "pos": "suffix",
  "senses": [
    {
      "categories": [
        "Latin entries with incorrect language header",
        "Latin lemmas",
        "Latin suffixes",
        "Pages with 4 entries",
        "Pages with entries"
      ],
      "glosses": [
        "Used for the second person present perfect singular form of any regular verb."
      ],
      "links": [
        [
          "second person",
          "second person#English"
        ],
        [
          "present perfect",
          "present perfect#English"
        ],
        [
          "singular",
          "singular#English"
        ]
      ],
      "tags": [
        "morpheme"
      ]
    }
  ],
  "word": "-isti"
}