also harelip, 1560s, from hare (n.) + lip (n.). So called for resemblance.
Entries linking to hare-lip
hare n.
Old English hara "hare," from Proto-West Germanic *hasan- (source also of Old Frisian hasa, Middle Dutch haese, Dutch haas, Old High German haso, German Hase), of uncertain origin; possibly the original sense was "gray" (compare Old English hasu, Old High German hasan "gray"), from PIE *khas- "gray" (source also of Latin canus "white, gray, gray-haired"). Perhaps cognate with Sanskrit sasah, Afghan soe, Welsh ceinach "hare." Rabbits burrow in the ground; hares do not.
þou hast a crokyd tunge heldyng wyth hownd and wyth hare. ["Jacob's Well," c. 1440]
lip n.
Old English lippa "lip, one of the two sides of the mouth," from Proto-Germanic *lepjan- (source also of Old Frisian lippa, Middle Dutch lippe, Dutch lip, Old High German lefs, German Lefze, Swedish läpp, Danish læbe). Boutkan and de Vaan reject the traditional IE derivation for this group and Latin labium, though they agree the Latin and Germanic words probably are related. It may be a substratum word. French lippe is an Old French borrowing from a Germanic source.
Transferred sense of "edge or margin of a cup, etc." is from 1590s. Slang sense "saucy talk" is from 1821, probably from the expression move the lip (1570s) "utter even the slightest word (against someone)." To bite (one's) lip "show vexation" is from early 14c. Stiff upper lip as a sign of courage and struggle against despondency is from 1833. Lip gloss is attested from 1939; lip balm from 1877. Related: Lips.