Greek ferry operator (6)
I believe the answer is:
charon
'greek ferry operator' is the definition.
The definition suggests a singular noun which matches the answer.
This is the entire clue.
Can you help me to learn more?
(Other definitions for charon that I've seen before include "Boatman across the river Styx" , "Hell's mythical boatman" , "He ferries dead over Styx" , "Mythological ferryman of the river Styx" , "Ferryman who brought the souls of the dead across the river Styx" .)