The Collaborative International Dictionary of English v.0.48:

combinative \combinative\ adj.
   1. produced by a combinatorial process. [Narrower terms:
      combinable, combinational, combinatory,
      combining(prenominal)] Also See: integrative. Antonym:
      noncombinative.
      [WordNet 1.5]

   2. able to combine; tending to combine. [Narrower terms:
      integrative (vs. disintegrative)]

   Syn: combinatory, combinatorial.
        [WordNet 1.5] combinatorial

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]