c. 1200, pece, "fixed amount, measure, portion;" c. 1300, "fragment of an object, bit of a whole, slice of meat; separate fragment, section, or part," from Old French piece "piece, bit portion; item; coin" (12c.), from Vulgar Latin *pettia, probably from Gaulish *pettsi (compare Welsh peth "thing," Breton pez "piece, a little"), perhaps from an Old Celtic base *kwezd-i-, from PIE root *kwezd- "a part, piece" (source also of Russian chast' "part"). Related: Pieces.
Meaning "separate article forming part of a class or group" is from c. 1400; that of "specimen, instance, example" is from 1560s. Sense of "portable firearm" is from 1580s, earlier "artillery weapon" (1540s). The meaning "chessman" is from 1560s. Meaning "a period of time" is from early 14c.; that of "a portion of a distance" is from 1610s; that of "literary composition" dates from 1530s.
Piece of (one's) mind "one's opinion expressed bluntly" is from 1570s. Piece of work "remarkable person" echoes Hamlet. Piece as "a coin" is attested in English from c. 1400, hence piece of eight, old name for the Spanish dollar (c. 1600) of the value of 8 reals and bearing a numeral 8. Adverbial phrase in one piece "whole, undivided, without loss or injury" is by 1580s; of a piece "as of the same piece or whole" is from 1610s.
c. 1400, pecen, "to mend (clothing) by adding pieces," from piece (n.1). Sense of "to join, unite or reunite, put together again" is from late 15c. Related: Pieced; piecing.
"a person, an individual," c. 1300, from piece (n.1), but in modern use contemptuous and commonly of women; the meaning "person regarded as a sex object" is by 1785. Compare piece of ass under ass (n.2); human beings colloquially have been piece of flesh from 1590s; also compare Latin scortum "bimbo, anyone available for a price," literally "skin."
PIECE. A wench. A damned good or bad piece; a girl who is more or less active and skilful in the amorous congress. Hence the (Cambridge) toast, may we never have a PIECE (peace) that will injure the constitution. [Dictionary of Buckish Slang, University Wit and Pickpocket Eloquence, London, 1811]
also codpiece, mid-15c., in male costume c. 1450-1550, a bagged appendage to the front of close-fitting breeches, "often conspicuous and ornamented" [OED], from Old English codd "a bag, pouch, husk," in Middle English, "testicles" (cognate with Old Norse koddi "pillow; scrotum") + piece (n.1).