Snake-haired monster such as Medusa (6)
I believe the answer is:
gorgon
(Other definitions for gorgon that I've seen before include "Ferocious woman" , "Unpleasant woman" , "In Greek myth, a snake-haired woman whose look turned watcher to stone" , "Petrifying woman of myth" , "Mythical Greek woman with snakes as hair" .)