c.1200, "fixed amount, measure, portion," from Old French piece "piece, bit portion; item; coin" (12c.), from Vulgar Latin *pettia, probably from Gaulish *pettsi (cf. Welsh peth "thing," Breton pez "piece, a little"), perhaps from an Old Celtic base *kwezd-i-, from PIE root *kwezd- "a part, piece" (cf. Russian chast' "part"). Related: Pieces.
Sense of "portable firearm" first recorded 1580s; that of "chessman" is from 1560s. Meaning "person regarded as a sex object" is first recorded 1785 (cf. piece of ass, human beings colloquially called piece of flesh from 1590s; cf. also Latin scortum "bimbo, anyone available for a price," literally "skin"). Meaning "a portion of a distance" is from 1610s; that of "literary composition" dates from 1530s. Piece of (one's) mind is from 1570s. Piece of work "remarkable person" echoes Hamlet. Piece as "a coin" is attested in English from 1570s, hence Piece of eight, old name for the Spanish dollar (c.1600) of the value of 8 reals.