Cutting fish, worker holds end of kipper (9)
I believe the answer is:
trenchant
'cutting' is the definition.
(I've seen this before)
'fish worker holds end of kipper' is the wordplay.
'fish' becomes 'tench' (tench is a kind of fish**).
'worker' becomes 'ant' (worker is a type of ant).
'holds' is an insertion indicator.
'end of' indicates one should take the final letters.
The final letter of 'kipper' is 'r'.
'tench'+'ant'='tenchant'
'tenchant' placed around 'r' is 'TRENCHANT'.
(Other definitions for trenchant that I've seen before include "Incisive in style" , "Vigorous and effective" , "Showing keenness" , "Acerbic" , "Keen" .)