Much of his life is spent behind bars (7)
I believe the answer is:
tapster
'much of his life is spent behind bars' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
This is the entire clue.
Can you help me to learn more?
(Other definitions for tapster that I've seen before include "Rat pest (anag.)" , "Bartender once" , "Old barperson" , "Bar employee" , "old barman" .)