The Collaborative International Dictionary of English v.0.48:

Theoretic \The`o*ret"ic\, Theoretical \The`o*ret"ic*al\, a. [Gr.
   ?: cf. L. theoreticus, F. th['e]or['e]tique.]
   Pertaining to theory; depending on, or confined to, theory or
   speculation; speculative; terminating in theory or
   speculation: not practical; as, theoretical learning;
   theoretic sciences. -- The`o*ret"ic*al*ly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

theoretical
    adj 1: concerned primarily with theories or hypotheses rather
           than practical considerations; "theoretical science"
           [syn: theoretical, theoretic] [ant: empiric,
           empirical]
    2: concerned with theories rather than their practical
       applications; "theoretical physics" [ant: applied]

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "theoretical":
   abstract, academic, analytical, armchair, closet, conceptual,
   conjectural, debatable, fanciful, hypothetic, hypothetical, ideal,
   idealized, ideational, ideological, impractical, moot, notional,
   postulatory, problematical, pure, putative, speculative,
   suppositional, supposititious, transcendent, transcendental,
   unproved, unproven, unrealistic, untested