WordNet (r) 3.0 (2006):

nonobservant
    adj 1: failing or refusing to observe religious customs

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "nonobservant":
   Laodicean, contrary, deviant, disregardful, dissenting, dissident,
   inattentive, inconstant, indevotional, indevout, indifferent,
   indifferentist, inobservant, lukewarm, negligent, nonadherent,
   noncompliant, nonconformable, nonconforming, nonreligious,
   recalcitrant, recusant, refractory, unadaptable, unadjustable,
   uncompliant, unconforming, undevout, undutiful, unfaithful,
   unloyal, unobservant, unreligious, unsubmissive, untrue