Source : Webster's Revised Unabridged Dictionary (1913)

Harelip \Hare"lip`\, n.
   A lip, commonly the upper one, having a fissure of
   perpendicular division like that of a hare. --
   {Hare"lipped`}, a.

Source : WordNet®

harelip
     n : a congenital cleft in the middle of the upper lip [syn: {cleft
         lip}, {cheiloschisis}]