Understands it's a gun - a woman's (7)
I believe the answer is:
gathers
'understands' is the definition.
('gather' can be a synonym of 'understand')
'a gun a woman's' is the wordplay.
'a gun' becomes 'gat' (gat is a kind of gun).
'a woman's' becomes 'hers' (her refers to a woman).
'gat'+'hers'='GATHERS'
'it's' is the link.
(Other definitions for gathers that I've seen before include "Collects in one place" , "Harvests" , "Draws together" , "The rags (anag.)" , "Part of dress" .)