Prison and one who should be in it? (7)
I believe the answer is:
brigand
'one who should be in it?' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'prison and' is the wordplay.
'prison' becomes 'brig' (I've seen this before).
'brig'+'and'='BRIGAND'
Can you help me to learn more?
(Other definitions for brigand that I've seen before include "Bandit" , "Outlaw" , "Marauder" , "Plunderer" , "Criminal" .)