Work quietly cutting fish in vain (7)
I believe the answer is:
foppish
'vain' is the definition.
(thesaurus)
'work quietly cutting fish' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'quietly' becomes 'p' (p for piano and quiet).
'cutting' is an insertion indicator (some letters cut their way into a word).
'op'+'p'='opp'
'opp' going into 'fish' is 'FOPPISH'.
'in' acts as a link.
(Other definitions for foppish that I've seen before include "Dandified" , "Dandyish" , "Affected" , "like Beau Brummell" , "Wet" .)