Cutting ditch with worker (9)
I believe the answer is:
trenchant
'cutting' is the definition.
(I've seen this before)
'ditch with worker' is the wordplay.
'ditch' becomes 'trench' (synonyms).
'with' says to put letters next to each other.
'worker' becomes 'ant' (worker is a type of ant).
'trench'+'ant'='TRENCHANT'
(Other definitions for trenchant that I've seen before include "Sharp" , "biting" , "Showing keenness" , "Forceful" , "Vigorous and effective" .)