The Collaborative International Dictionary of English v.0.48:

Unlike \Un*like"\, a.
   1. Not like; dissimilar; diverse; having no resemblance; as,
      the cases are unlike.
      [1913 Webster]

   2. Not likely; improbable; unlikely. [Obsoles.]
      [1913 Webster]

   Unlike quantities (Math.), quantities expressed by letters
      which are different or of different powers, as a, b, c,
      a^2, a^3, x^n, and the like.

   Unlike signs (Math.), the signs plus (+) and minus (-).
      [1913 Webster]