Source : Webster's Revised Unabridged Dictionary (1913)

Preform \Pre*form"\, v. t. [L. praeformare. See {Pre-}, and
   {Form}.]
   To form beforehand, or for special ends. ``Their natures and
   preformed faculties. '' --Shak.

Source : WordNet®

preform
     v 1: form into a shape resembling the final, desired one
     2: form or shape beforehand or determine the shape of
        beforehand