bargain: [14] Bargain appears to be distantly related to borrow. Its immediate source was Old French bargaignier ‘haggle’, but this was probably borrowed from Germanic *borganjan, a derivative of *borgun (from which ultimately we get borrow). The sense development may have been as follows: originally ‘look after, protect’ (the related Germanic *burg- produced English borough, which to begin with meant ‘fortress’, and bury); then ‘take on loan, borrow’; then ‘take or give’; and hence ‘trade, haggle, bargain’. => belfrey, borough, borrow, bury
bargain (v.)
late 14c., from Old French bargaignier (12c., Modern French barguigner) "to haggle over the price," perhaps from Frankish *borganjan "to lend" or some other Germanic source, ultimately from Proto-Germanic *borgan (cognates: Old High German borgen; Old English borgian, source of borrow). Another suggestion is that the French word comes from Late Latin barca "a barge," because it "carries goods to and fro." There are difficulties with both suggestions. Related: Bargained; bargaining.
bargain (n.)
mid-14c., "business transaction or agreement," also "that which is acquired by bargaining," from Old French bargaine, from bargaignier (see bargain (v.)). Meaning "article priced for special sale" is from 1899. A bargain basement (1899) originally was a basement floor in a store where bargains were displayed.