Translation:He comes and she comes. They come.
There you have the source: https://www.focloir.ie/en/dictionary/ei/come#come__10
Yes, Irish speakers who use this expression in English have adopted it as a literal translation in Irish.
It's the kind of terminology and usage that wouldn't have made it in to early dictionaries. I don't know if the technical term sead was used in the vernacular.
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