A cleft lip; so called from its resemblance to the upper lip of a hare. It was said to be the mischievous act of an elf or malicious fairy.
“This is the foul flend Flibbertigibbet. He begins at curfew, and
walks till the first cock. He ... squints the eye and makes the
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894