Prisoner given shelter is happy (7)
I believe the answer is:
content
'happy' is the definition.
('content' is associated in meaning with 'happy')
'prisoner given shelter' is the wordplay.
'prisoner' becomes 'con' (abbreviation for 'convict').
'given' means one lot of letters go next to another.
'shelter' becomes 'tent' (tent is a kind of shelter).
'con'+'tent'='CONTENT'
'is' acts as a link.
(Other definitions for content that I've seen before include "Gist" , "Satisfied - subject matter" , "Quietly happy" , "Satisfied, happy enough" , "Satisfied - all within - capacity" .)