He has a paying job in store (5)
I believe the answer is:
buyer
This could be a double definition.
'he has a paying' is the first definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'job in store' is the second definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
Can you help me to learn more?
(Other definitions for buyer that I've seen before include "One forking out money" , "Selector of stock" , "store employee" , "A purchaser, maybe for firm" , "Caveat emptor - . . . . . beware" .)