ˈboastfully,adv. [f.prec. + -ly2.] In a boastful manner; vauntingly. c1430Life St. Kath. (Gibbs MS.) 55 Wher yn bostfully she enhaunceth hir self.1845Ld. Campbell Chancellors (1857) III. li. 4 Observing boastfully, ‘We inherit all our genius from our mother’.