A sailor scowls about Herculean tasks (7)
I believe the answer is:
labours
'herculean tasks' is the definition.
The answer and definition can be both acts as well as being plural nouns.
Maybe they are linked in a way I don't understand?
'a sailor scowls about' is the wordplay.
'a sailor' becomes 'ab' (abbreviation for able seaman).
'scowls' becomes 'lours' (I can't explain this - if you can you should give a lot more credence to this answer).
'about' is an insertion indicator.
'ab' put into 'lours' is 'LABOURS'.
Can you help me to learn more?
(Other definitions for labours that I've seen before include "Works hard and makes great efforts" , "Overemphasises" , "Hercules underwent 12 of them" , "Hercules had twelve" , "Shakespeare: 'Love's . . . . . . . Lost'" .)