Brag
Middle English (as an adjective in the sense ‘boastful’): of unknown origin (French braguer is recorded only later).
wiktionary
From Middle English braggen(“to make a loud noise; to speak boastfully”) of unknown origin. Possibly related to the Middle English adjective brag(“prideful; spirited”), which is probably of Celtic origin; [1] or from Old Norse bragr(“best; foremost; poetry”); [2] or through Old English from Old Norse braka(“to creak”). [3]
etymonline
brag (v.)
late 14c., braggen "to make a loud sound," also "to talk boastfully," of obscure origin, perhaps related to bray of a trumpet and imitative, or related to the Middle English adjective brag "ostentatious, proud; spirited, brave" (early 14c.), which probably is from Celtic, and is the source of the surname Bragg (attested from mid-13c.). Perhaps a merger of the two. Other sources suggest Old Norse bragr "the best, the toast (of anything)," also "poetry." Also see braggart for another possibility, but French brague seems too late to be the source. Related: Bragged; bragging.
brag (n.)
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.
