The Collaborative International Dictionary of English v.0.48:

Suppositive \Sup*pos"i*tive\, a. [Cf. F. suppositif.]
   Including or implying supposition, or hypothesis; supposed.
   -- Sup*pos"i*tive*ly, adv. --Hammond.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Suppositive \Sup*pos"i*tive\, n.
   A word denoting or implying supposition, as the words if,
   granting, provided, etc. --Harris.
   [1913 Webster]