The Collaborative International Dictionary of English v.0.48:

Incompatible \In`com*pat"i*ble\, a. [Pref. in- not + compatible:
   cf. F. incompatible.] [It was formerly sometimes written
   incompetible.]
   [1913 Webster]
   1. Not compatible; so differing as to be incapable of
      harmonious combination or coexistence; inconsistent in
      thought or being; irreconcilably disagreeing; as, persons
      of incompatible tempers; incompatible colors, desires,
      ambition.
      [1913 Webster]

            A strength and obduracy of character incompatible
            with his meek and innocent nature.    --Southey.
      [1913 Webster]

   2. (Chem.) Incapable of being together without mutual
      reaction or decomposition, as certain medicines.
      [1913 Webster]

   Incompatible terms (Logic), terms which can not be combined
      in thought.

   Syn: Inconsistent; incongruous; dissimilar; irreconcilable;
        unsuitable; disagreeing; inharmonious; discordant;
        repugnant; contradictory. See Inconsistent.
        [1913 Webster]