The Collaborative International Dictionary of English v.0.48:
Mordacious \Mor*da"cious\, a. [L. mordax, -acis, fr. mordere, morsum, to bite. See Morsel.] Biting; given to biting; hence, figuratively, sarcastic; severe; scathing. -- Mor*da"cious*ly, adv. [1913 Webster]WordNet (r) 3.0 (2006):
mordaciously adv 1: in a mordacious manner; "she taunted him mordaciously"