Arsenal reserves warm up (4)
I believe the answer is:
guns
'arsenal reserves' is the definition.
Although both the answer and definition are verbs in their -s form, I don't see how one could define the other.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for guns that I've seen before include "Firearms" , "Snug weapons?" , "Transportable armaments" , "Bangers" .)