Source : Webster's Revised Unabridged Dictionary (1913)

Unifacial \U`ni*fa"cial\, a. [Uni- + facial.]
   Having but one front surface; as, some foliaceous corals are
   unifacial, the polyp mouths being confined to one surface.

Source : WordNet®

unifacial
     adj : having but one principal or specialized surface; "a
           primitive unifacial flint tool"