Enjoy a bit of fun in port (5)
I believe the answer is:
haven
'port' is the definition.
(both can mean a place of safety)
'enjoy a bit of fun' is the wordplay.
'enjoy' becomes 'have' (to enjoy can mean have or have use of).
'a bit of fun' becomes 'n' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'have'+'n'='HAVEN'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for haven that I've seen before include "Safe refuge" , "Place of shelter" , "Anchorage - retreat" , "A peaceful refuge" , "Harbour, small port" .)