Taking part in duel, I'm in a temper — kill! (9)
I believe the answer is:
eliminate
'kill' is the definition.
(eliminating is a kind of killing)
'taking part in duel i'm in a temper' is the wordplay.
'taking part in' indicates a hidden word.
'ELIMINATE' is hidden within 'duel im in a temper'.
(Other definitions for eliminate that I've seen before include "Take out" , "Exclude from further stage of competition" , "Annihilate" , "Do away with, remove" , "put out" .)