Source : Webster's Revised Unabridged Dictionary (1913)

Suppositional \Sup`po*si"tion*al\, a.
   Resting on supposition; hypothetical; conjectural; supposed.
   --South.

Source : WordNet®

suppositional
     adj : based primarily on surmise rather than adequate evidence;
           "theories about the extinction of dinosaurs are still
           highly conjectural"; "the supposed reason for his
           absence"; "suppositious reconstructions of dead
           languages"; "supposititious hypotheses" [syn: {conjectural},
            {divinatory}, {supposed}, {suppositious}, {supposititious}]