Fish not doing very much (6)
I believe the answer is:
idling
'very much' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'fish not doing' is the wordplay.
I cannot really see how this works, but
'fish' could be 'ling' (ling is a kind of fish) and 'ling' is found within the answer.
The remaining letters 'id' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for idling that I've seen before include "(Engine) ticking over" , "Spending time doing nothing" , "'Lazing, loafing (6)'" , "Loafing or just ticking over" , "Not in gear; lazing around" .)