Jack has trouble in prison (4)
I believe the answer is:
jail
'prison' is the definition.
(jail can mean a prison)
'jack has trouble' is the wordplay.
'jack' becomes 'J' (playing card abbreviation).
'has' means one lot of letters go next to another.
'trouble' becomes 'ail' (synonyms).
'j'+'ail'='JAIL'
'in' is the link.
(Other definitions for jail that I've seen before include "sentence" , "Correctional institution" , "Gaol" , "Cooler" , "place for punishment" .)