Prepared to fire with very little justification (7-5)
I believe the answer is:
trigger-happy
'prepared' is the definition.
Both the definition and answer are adjectives. Perhaps there's an association between them I don't understand?
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for trigger-happy that I've seen before include "Quick to use a gun" , "Over-ready to shoot" , "Over-enthusiastic with a gun" , "Irresponsible with firearms" , "inclined to recklessness" .)