WordNet (r) 3.0 (2006):

back talk
    n 1: an impudent or insolent rejoinder; "don't give me any of
         your sass" [syn: sass, sassing, backtalk, back
         talk, lip, mouth]

Moby Thesaurus II by Grady Ward, 1.0:

43 Moby Thesaurus words for "back talk":
   acknowledgment, answer, answering, antiphon, back answer, backchat,
   cheek, comeback, echo, evasive reply, guff, impudence, insolence,
   jaw, lip, mouth, reaction, ready reply, receipt, rejoinder,
   repartee, replication, reply, repost, rescript, rescription,
   respondence, response, responsion, responsory, retort, return,
   reverberation, riposte, sass, sassiness, sauce, sauciness,
   short answer, snappy comeback, witty reply, witty retort,
   yes-and-no answer