The Collaborative International Dictionary of English v.0.48:

combinatorial \combinatorial\ combinatory \combinatory\adj.
   1. able to combine; tending to combine.

   Note: same as combinative, 2. [Narrower terms: integrative
         (vs. disintegrative)]

   Syn: combinative.
        [WordNet 1.5]

   2. of or relating to combinations. [Narrower terms:
      combinative (vs. noncombinative)] WordNet 1.5]

   3. produced by a process of combining; as, a combinatorial
      explosion of possibilities; -- used especially in
      reference to mathematical or statistical processes of
      computing possible combinations.
      PJC]

WordNet (r) 3.0 (2006):

combinatorial
    adj 1: relating to or involving combinations [syn:
           combinative, combinatory, combinatorial]
    2: relating to the combination and arrangement of elements in
       sets