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):

hypothetically
    adv 1: by hypothesis