Went out with old hat (5)
I believe the answer is:
dated
I believe this clue is a triple definition!
'went out with' is the first definition.
('date' can be a synonym of 'go out with')
'old' is the second definition.
(dated can mean old or out of date)
'hat' is the third definition.
(I have seen 'Old hat' mean 'dated' so perhaps 'hat' could also mean 'dated')
(Other definitions for dated that I've seen before include "Pass" , "Out of fashion" , "No longer fashionable or current" , "not without romantic engagements" , "Rusty" .)