The Collaborative International Dictionary of English v.0.48:

Brag \Brag\, v. i. [imp. & p. p. Bragged; p. pr. & vb. n.
   Bragging.] [OE. braggen to resound, blow, boast (cf. F.
   braguer to lead a merry life, flaunt, boast, OF. brague
   merriment), from Icel. braka to creak, brak noise, fr. the
   same root as E. break; properly then, to make a noise, boast.
   ?95.]
   To talk about one's self, or things pertaining to one's self,
   in a manner intended to excite admiration, envy, or wonder;
   to talk boastfully; to boast; -- often followed by of; as, to
   brag of one's exploits, courage, or money, or of the great
   things one intends to do.
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         Conceit, more rich in matter than in words,
         Brags of his substance, not of ornament. --Shak.
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   Syn: To swagger; boast; vapor; bluster; vaunt; flourish; talk
        big.
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