Etymology Clipping of brassiere, borrowed from French brassière, from Old French braciere (originally a lining inside armor to protect the arm, but later a garment), from Old French brace (“arm”), from Latin bracchia, plural of Latin bracchium (“forearm”), from Ancient Greek βραχίων (brakhíōn, “forearm”), from Proto-Hellenic *brəkʰús (“short”) (because the forearm is shorter than the upper arm), inherited from Proto-Indo-European *mréǵʰus.
1
An item of clothing, usually underwear worn to support the breasts.
Mary felt annoyed at the girl; just because bras had become passé, did a girl with so pronounced a bosom have to cater to fashion? In this case practicality dictated a bra, and Mary stood at the desk feeling herself flushing with disapproval.1964, Philip K. Dick, “FOUR”, in Clans of the Alphane Moon, United States: Ace Books, →OCLC; republished London: HarperCollinsPublishers, 1996, →ISBN, page 27:
Her housecoat had fallen open. She was wearing only panties and bra, which did nothing to make her scrawny, wrinkled body appealing.1968, Carl Ruhen, The Key Club, Sydney: Scripts, page 12:
Etymology From bracket, referring to the notation introduced in 1939 by Paul Dirac.
1
Linear algebra, Mathematics, Sciences One of the two vectors in the standard notation for describing quantum states in quantum mechanics, the row vector; the other (column) vector being its complex conjugate, the ket.