In good order, arms given up (4)
I believe the answer is:
snug
'in good order' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'arms given up' is the wordplay.
'arms' becomes 'guns' (gun is a kind of arm).
'given up' is a reversal indicator (in a down clue, letters go up).
'guns' in reverse letter order is 'SNUG'.
Can you help me to learn more?
(Other definitions for snug that I've seen before include "joiner" , "Close-fitting and cosy" , "Small bar in pub - warm and comfortable" , "Comfortable with guns" , "Comfortable -- small secluded room" .)