Only the men are up in arms (4)
I believe the answer is:
stag
'arms' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for stag that I've seen before include "speculator wanting quick profit" , "Excluding women" , "Stock market speculator" , "Hart" , "One who speculates" .)