c. 1500 shortening of Middle English ampte (late 14c.), from Old English æmette "ant," from West Germanic *emaitjon (source also of Old High German ameiza, German Ameise) from a compound of Germanic *e-, *ai- "off, away" + *mai- "cut," from PIE root *mai- (1) "to cut" (see maim). Thus the insect's name is, etymologically, "the biter-off."
As þycke as ameten crepeþ in an amete hulle [chronicle of Robert of Gloucester, 1297]Emmet survived into 20c. as an alternative form. White ant "termite" is from 1729. To have ants in one's pants "be nervous and fidgety" is from 1934, made current by a popular song; antsy embodies the same notion.