Stallion or stag (4)
I believe the answer is:
male
This clue is a double definition.
'stallion' is the first definition.
(I've seen this in another clue)
'stag' is the second definition.
(a stag is a male deer)
(Other definitions for male that I've seen before include "A gender" , "man?" , "Maldives capital; masculine" , "As are drakes, bulls etc." , "Lame sort of fellow" .)