The Collaborative International Dictionary of English v.0.48:

Harelip \Hare"lip`\ (h[^a]r"l[i^]p`), n.
   A lip, commonly the upper one, having a fissure of
   perpendicular division like that of a hare. -- Hare"lipped`
   (-l[i^]pt`), a.
   [1913 Webster]

WordNet (r) 3.0 (2006):

harelip
    n 1: a congenital cleft in the middle of the upper lip [syn:
         cleft lip, harelip, cheiloschisis]

Moby Thesaurus II by Grady Ward, 1.0:

30 Moby Thesaurus words for "harelip":
   bowlegs, camelback, cleft palate, clubfoot, crookback, defacement,
   deformation, deformity, disfigurement, flatfoot, freakishness,
   humpback, hunchback, knock-knee, kyphosis, lordosis,
   malconformation, malformation, misproportion, misshape,
   monstrosity, mutilation, splayfoot, swayback, talipes, teratology,
   torticollis, truncation, valgus, wryneck