late 14c., "pomp; arrogance, pride;" see brag, v.; the exact relationship of the forms is uncertain. Meaning "that which is boasted" is from 1530s. As a once-popular poker-like card game, from 1734.

mid-14c., braggen "to make a loud sound," also "to talk boastfully," of obscure origin, perhaps related to bray of a trumpet, or related to the Middle English adjective brag "ostentatious, proud; spirited, brave" (early 14c.), which probably is from Celtic. Other sources suggest Old Norse bragr "the best, the toast (of anything)," also "poetry." Also see braggart for another possibility. Related: Bragged; bragging.