Source : Webster's Revised Unabridged Dictionary (1913)

Impious \Im"pi*ous\, a. [L. impius; pref. im- not + pius piou.
   See {Pious}.]
   Not pious; wanting piety; irreligious; irreverent; ungodly;
   profane; wanting in reverence for the Supreme Being; as, an
   impious deed; impious language.

         When vice prevails, and impious men bear away, The post
         of honor is a private station.           --Addison.

   Syn: {Impious}, {Irreligious}, {Profane}.

   Usage: Irreligious is negative, impious and profane are
          positive. An indifferent man may be irreligious; a
          profane man is irreverent in speech and conduct; an
          impious man is wickedly and boldly defiant in the
          strongest sense. Profane also has the milder sense of
          secular. --C. J. Smith. -- {Im"pi*ous*ly}, adv. --
          {Im"pi*ous*ness}, n.

Source : WordNet®

impious
     adj 1: lacking piety or reverence for a god [ant: {pious}]
     2: lacking due respect or dutifulness; "impious toward one's
        parents"; "an undutiful son" [syn: {undutiful}]
     3: lacking piety and reverence for a god [syn: {ungodly}]