Gorgon

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Greek Mythology Any of the three sisters Stheno, Euryale, and the mortal Medusa who had snakes for hair and eyes that if looked into turned the beholder into stone.
• noun A woman regarded as ugly or terrifying.

from The Century Dictionary.

• noun [capitalized] In Greek myth, a female monster, one of three sisters, Stheno, Euryale, and Medusa, whose heads were covered with writhing serpents instead of hair, and the sight of whose terrific aspect turned the beholder to stone. Only Medusa was mortal, and she alone is meant when the Gorgon is mentioned singly.
• noun The head of Medusa, after she was killed by Perseus, placed on the shield of Pallas, and, according to the legend, still capable of petrifying beholders; hence, a representation of Medusa's head; a gorgoneion.
• noun Something very ugly; specifically, a woman of repulsive appearance or manners.
• noun A type of direct-acting marine engine for paddle-steamers. See marine engine, under marine.
• noun A name, generic or specific, of the brindled gnu. Also Gorgonia.
• Like one of the Gorgons; pertaining to a gorgon; very ugly or repulsive.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Gr. Myth.) One of three fabled sisters, Stheno, Euryale, and Medusa, with snaky hair and of terrific aspect, the sight of whom turned the beholder to stone. The name is particularly given to Medusa.
• noun Anything very ugly or horrid.
• noun (Zoöl.) The brindled gnu. See Gnu.
• adjective Like a Gorgon; very ugly or terrific.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (Greek mythology) any of three winged sister monsters and the mortal Medusa who had live snakes for hair; a glance at Medusa turned the beholder to stone