Source : Webster's Revised Unabridged Dictionary (1913)

Necessitarian \Ne*ces`si*ta"ri*an\, a.
   Of or pertaining to the doctrine of philosophical necessity
   in regard to the origin and existence of things, especially
   as applied to the actings or choices of the will; -- opposed
   to {libertarian}.

Necessitarian \Ne*ces`si*ta"ri*an\, n.
   One who holds to the doctrine of necessitarianism.

Source : WordNet®

necessitarian
     n : someone who does not believe the doctrine of free will [ant:
          {libertarian}]