Greek hero’s painstaking, sick (8)
I believe the answer is:
achilles
'greek hero's' is the definition.
(I've seen this before)
'painstaking sick' is the wordplay.
I cannot quite see how this works, but
'sick' could be 'ill' (similar in meaning) and 'ill' is present in the answer.
The remaining letters 'aches' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for achilles that I've seen before include "Heroic warrior" , "Legendary Greek with injured heel" , "Homeric hero" , "Greek hero with vulnerable heel" , "Legendary Greek hero with weak heel" .)