E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Anything unusually hideous. There were three Gorgons, with serpents on their heads instead of hair: Medusa was the chief of the three, and the only one that was mortal; but so hideous was her face that whoever set eyes on it was instantly turned into stone. She was slain by Perseus, and her head placed on the shield of Minerva.
Lest Gorgon rising from the infernal lakes
With horrors armed, and curls of hissing snakes,
Should fix me, stiffened at the monstrous sight,
A stony image in eternal night.
What was that snaky-headed Gorgon shield
That wise Minerva wore, unconquered virgin,
Wherewith she freezed her foes to congealed stone?