Source : Webster's Revised Unabridged Dictionary (1913)

Cowlick \Cow"lick`\ (-l?k`), n.
   A tuft of hair turned up or awry (usually over the forehead),
   as if licked by a cow.

Source : WordNet®

cowlick
     n : a tuft of hair that grows in a different direction from the
         rest of the hair and usually will not lie flat