Gorgon slain by Perseus (6)
I believe the answer is:
medusa
'gorgon slain by perseus' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for medusa that I've seen before include "Amused by the mythical gorgon?" , "Mythical woman with snakes for hair" , "all her visitors got stoned" , "Form of jellyfish" , "Gorgon with snakes for hair" .)