Medusa's slayer (7)
I believe the answer is:
perseus
'medusa's slayer' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for perseus that I've seen before include "'Having slain Medusa, he became a constellation (7)'" , "Group of stars" , "Hero who killed Medusa" , "Gorgon-slayer and rescuer of Andromeda" , "Son of Zeus" .)