The Collaborative International Dictionary of English v.0.48:

Incommensurate \In`com*men"su*rate\, a.
   1. Not commensurate; not admitting of a common measure;
      incommensurable.
      [1913 Webster]

   2. Not of equal of sufficient measure or extent; not
      adequate; as, our means are incommensurate to our wants.

   Syn: Inadequate; insufficient; disproportionate. --
        In`com*men"su*rate*ly, adv. --
        In`com*men"su*rate*ness, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

incommensurate
    adj 1: not corresponding in size or degree or extent; "a reward
           incommensurate with his effort" [ant: commensurate]