Source : Webster's Revised Unabridged Dictionary (1913)

Perforce \Per*force"\, adv. [F. par (L. per) + force.]
   By force; of necessary; at any rate. --Shak.

Perforce \Per*force"\, v. t.
   To force; to compel. [Obs.]

Source : WordNet®

perforce
     adv : by necessity; by force of circumstance