The Collaborative International Dictionary of English v.0.48:

Necessarian \Nec`es*sa"ri*an\, n. [Cf. F. n['e]cessarien. See
   Necessary.]
   An advocate of the doctrine of philosophical necessity; a
   necessitarian.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Necessarian \Nec`es*sa"ri*an\, a.
   Of or pertaining to necessarianism.
   [1913 Webster]