mooncalf

A mooncalf (or moon-calf) is a monstrous birth, the abortive fetus of a cow or other farm animal. The term was occasionally applied to an abortive human fetus.

The term derives from the once widespread superstition, present in many European folk traditions, that such malformed creatures were the product of the sinister influence of the Moon on fetal development. The earliest recorded use of the term was in 1565, referring to a human false pregnancy.