Source : Webster's Revised Unabridged Dictionary (1913)

Apologist \A*pol"o*gist\, n. [Cf. F. apologiste.]
   One who makes an apology; one who speaks or writes in defense
   of a faith, a cause, or an institution; especially, one who
   argues in defense of Christianity.

Source : WordNet®

apologist
     n : a person who argues to defend or justify some policy or
         institution; "an apologist for capital punishment" [syn:
         {vindicator}, {justifier}]