brag:  Brag first turned up in English as an adjective, meaning ‘spirited’ or ‘boastful’; the verb and noun did not appear until the 14th century. Where English got the word from, however, remains a mystery. French has braguer ‘brag’, but it is not clear whether English borrowed from French, or vice versa; French did, however, contribute the derivative bragard, which English adopted as braggart . This probably also formed the basis of braggadocio, an Italianate coinage first used by the poet Edmund Spenser as a personification of ‘boastfulness’ in his Faerie Queene 1590.
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.