The Collaborative International Dictionary of English v.0.48:

Hypothetic \Hy`po*thet"ic\, Hypothetical \Hy`po*thet"ic*al\, a.
   [L. hypotheticus, Gr. ?: cf. F. hypoth['e]tique.]
   Characterized by, or of the nature of, an hypothesis;
   conditional; assumed without proof, for the purpose of
   reasoning and deducing proof, or of accounting for some fact
   or phenomenon.
   [1913 Webster]

         Causes hypothetical at least, if not real, for the
         various phenomena of the existence of which our
         experience informs us.                   --Sir W.
                                                  Hamilton.
   [1913 Webster]

   Hypothetical baptism (Ch. of Eng.), baptism administered to
      persons in respect to whom it is doubtful whether they
      have or have not been baptized before. --Hook. --
      Hy`po*thet"ic*al*ly, adv. --South.
      [1913 Webster]

WordNet (r) 3.0 (2006):

hypothetical
    adj 1: 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"; "hypothetical situation" [syn: conjectural,
           divinatory, hypothetical, hypothetic, supposed,
           suppositional, suppositious, supposititious]
    n 1: a hypothetical possibility, circumstance, statement,
         proposal, situation, etc.; "consider the following, just as
         a hypothetical"

Moby Thesaurus II by Grady Ward, 1.0:

48 Moby Thesaurus words for "hypothetical":
   a fortiori, a posteriori, a priori, abstract, academic, analytic,
   armchair, assumed, categorical, conditional, conjectural,
   conjectured, deductive, dialectic, discursive, doubtful,
   enthymematic, epagogic, guessed, hypothesized, hypothetic, ideal,
   imagined, impractical, inductive, inferential, maieutic, moot,
   notional, postulatory, presumed, problematic, putative, reputed,
   soritical, speculative, supposed, suppositional, supposititious,
   suppositive, suppository, surmised, suspected, syllogistic,
   synthetic, theoretical, transcendent, transcendental