Not at home in Southampton (3)
I believe the answer is:
out
'not at home' is the definition.
(out can mean away from home)
'in southampton' is the wordplay.
'in' says the answer is hidden in the clue.
'OUT' is hidden within 'southampton'.
(Other definitions for out that I've seen before include "For example, caught" , "Old hat" , "Published; unconscious" , "See 19" , "Means of escape" .)