The Collaborative International Dictionary of English v.0.48:

Combinable \Com*bin"a*ble\, a. [Cf. F. combinable.]
   Capable of combining; consistent with. [R.] --M. Arnold. --
   Com*bin"a*ble*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

combinable
    adj 1: able to or tending to combine [syn: combinable,
           combinational, combinatory]