Bit of lethal force (4)
I believe the answer is:
half
'bit' is the definition.
(I know that half is a type of bit)
'of lethal force' is the wordplay.
'of' indicates a hidden word.
'HALF' is hidden in the letters of 'lethal force'.
(Other definitions for half that I've seen before include "Fifty per cent" , "Two of these to the pint" , "Two of which make the whole" , "Fifty percent" , "0.5" .)