Herculean chore involves stop at sea (6)
I believe the answer is:
anchor
'stop at sea' is the definition.
(to anchor a boat is to stop it)
'herculean chore involves' is the wordplay.
'involves' says the answer is hidden in the clue.
'ANCHOR' is hidden in the letters of 'herculean chore'.
(Other definitions for anchor that I've seen before include "Fix securely" , "Holding device for ship" , "Set fast" , "TV journalist" , "Weigh down" .)