Fighting words: grenade exploding! (2,5)
I believe the answer is:
en garde
'fighting words' is the definition.
'en garde' can be an answer for 'words' (I have seen 'Words of warning' mean 'en garde' so perhaps 'words' could also mean 'en garde'). I am not certain of the 'fighting' bit.
'grenade exploding' is the wordplay.
'exploding' indicates an anagram.
'grenade' anagrammed gives 'EN GARDE'.
Can you help me to learn more?
(Other definitions for en garde that I've seen before include "Words of warning" , "Warning cry in fencing" , "Fencer's call" , "Fencer's warning cry" , "Prepare to fence!" .)