E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
is an inanimate, shapeless mass (Pliny: Natural History, x. 64). This abortion was supposed to be produced by the influence of the moon. The primary meaning of calf is not the young of a cow, but the issue arising from throwing out, as a push, a protuberance; hence the calves of the legs.
A false conception, called mola, i.e. moon-calf a lump of flesh without shape or life.Holland: Pliny, vii. 15.