Cutting fish, worker holds kipper's tail (9)
I believe the answer is:
trenchant
'cutting' is the definition.
(I've seen this before)
'fish worker holds kipper's tail' 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.
'tail' suggests the final letters.
The final letter of 'kipper' is 'r'.
'tench'+'ant'='tenchant'
'tenchant' enclosing 'r' is 'TRENCHANT'.
(Other definitions for trenchant that I've seen before include "biting" , "Clear-cut and hard-hitting" , "Acerbic" , "Clear" , "Expressively incisive" .)