The Collaborative International Dictionary of English v.0.48:

Unify \U"ni*fy\, v. t. [imp. & p. p. Unified; p. pr. & vb. n.
   Unifying.] [Uni- + -fy: cf. F. unifier.]
   To cause to be one; to make into a unit; to unite; to view as
   one.
   [1913 Webster]

         A comprehensive or unifying act of the judging faculty.
                                                  --De Quincey.
   [1913 Webster]

         Perception is thus a unifying act.       --Sir W.
                                                  Hamilton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

unifying
    adj 1: combining into a single unit [syn: consolidative,
           unifying]
    2: tending to unify [syn: centripetal, unifying(a)]