Coming back with "Nonsense, you chump, he's a clergyman!" (6)
I believe the answer is:
pastor
This clue might be a double definition.
'coming back with nonsense you chump he's' is the first definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'a clergyman' is the second definition.
(pastor is a kind of clergyman)
Can you help me to learn more?
(Other definitions for pastor that I've seen before include "Minister; shepherd" , "To spar with clergyman" , "Church minister" , "Padre perhaps" , "Minister of religion" .)