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

WordNet (r) 3.0 (2006):

combinative
    adj 1: marked by or relating to or resulting from combination
           [syn: combinative, combinatory] [ant:
           noncombinative]
    2: relating to or involving combinations [syn: combinative,
       combinatory, combinatorial]