Styx ferryman (6)
I believe the answer is:
charon
'styx ferryman' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for charon that I've seen before include "Nineteen across of Pluto; Styx ferryman; anchor (anag.)" , "Ferryman on river of Hades" , "He ferries dead over Styx" , "Mythical boatman of the River Styx" , "Boatman across the river Styx" .)