braggart (n.)

also -art, from Old French -ard, -art, from German -hard, -hart "hardy," forming the second element in many personal names, often used as an intensifier, but in Middle High German and Dutch used as a pejorative element in common nouns, and thus passing into Middle English in bastard, coward, blaffard ("one who stammers"), etc. It thus became a living element in English, as in buzzard, drunkard. The German element is from Proto-Germanic *-hart/*-hard "bold, hardy" (from PIE root *kar- "hard").

1570s, bragget, "architectural support, supporting piece projecting from a vertical surface," probably from French braguette, originally "codpiece armor" (16c.), from a fancied resemblance of architectural supports to that article of attire (Spanish cognate bragueta meant both "codpiece" and "projecting moulding in architecture"), diminutive of brague "knee pants," ultimately from Gaulish *braca "pants," itself perhaps from Germanic (compare Old English broc "garment for the legs and trunk;" see breeches).

The architectural meaning also might be directly from the "breeches" sense, on the notion of two limbs or of appliances used in pairs. The senses have been affected by Latin brachium "arm." The typographical bracket ("marks used to enclose a note, reference, explanation, etc.;" each was formerly a crotchet) is in use by 1750, so called for its resemblance to double supports in carpentry (a sense attested from 1610s). The meaning "position of being enclosed or bracketed with others" as of equal standing is from 1880.

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.