It may be trained to kill (5)
I believe the answer is:
rifle
'it may be trained to kill' is the definition.
The definition suggests a singular noun which matches the answer.
This is the entire clue.
Can you help me to learn more?
(Other definitions for rifle that I've seen before include "Long-barrelled weapon, normal army equipment" , "Firearm - plunder" , "Gun; thoroughly search" , "Pillage; a weapon" , "Gun - ransack" .)