Source : Webster's Revised Unabridged Dictionary (1913)

Unchristian \Un*chris"tian\, a. [Pref. un- not + Christian.]
   1. Not Christian; not converted to the Christian faith;
      infidel.

   2. Contrary to Christianity; not like or becoming a
      Christian; as, unchristian conduct.

Unchristian \Un*chris"tian\, v. t. [1st pref. un- + Christian.]
   To make unchristian. [Obs.] --South.

Source : WordNet®

unchristian
     adj : not of a Christian faith [ant: {christian}]