Let go of a French assistant (6)
I believe the answer is:
unhand
'let go of' is the definition.
(unhanding is a kind of letting go of)
'a french assistant' is the wordplay.
'a french' becomes 'un' ('a' in French).
'assistant' becomes 'hand' (hand can mean a worker or employee).
'un'+'hand'='UNHAND'
(Other definitions for unhand that I've seen before include "Let go of, remove grasp" , "Physically let go" , "Release" .)