Part of lethal force (4)
I believe the answer is:
half
'part' is the definition.
(thesaurus)
'of lethal force' is the wordplay.
'of' says the answer is hidden in the clue.
'HALF' is hidden in the letters of 'lethal force'.
(Other definitions for half that I've seen before include "0.5" , "one over a couple" , "Moiety" , "Short distance - steal!" , "Some football" .)