The Collaborative International Dictionary of English v.0.48:

Undutiful \Undutiful\
   See dutiful.

WordNet (r) 3.0 (2006):

undutiful
    adj 1: lacking due respect or dutifulness; "impious toward one's
           parents"; "an undutiful son" [syn: impious,
           undutiful]

Moby Thesaurus II by Grady Ward, 1.0:

43 Moby Thesaurus words for "undutiful":
   Laodicean, apostate, atheistic, backsliding, blasphemous,
   disobedient, fallen, fallen from grace, froward, impious,
   indevotional, indevout, indifferent, indifferentist, indisciplined,
   irreligious, irreverent, lapsed, lawless, lukewarm, naughty,
   nonconforming, nonobservant, nonreligious, obstinate, profanatory,
   profane, recidivist, recidivistic, recreant, recusant, renegade,
   sacrilegious, self-willed, transgressive, uncomplying, undevout,
   undisciplined, unduteous, unreligious, violative, wayward,
   willful