Couldn't you listen to him for a fiver? (5)
I believe the answer is:
tenor
'couldn't you listen to him for a fiver?' 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 tenor that I've seen before include "Highest male voice" , "Eg, Luciano Pavarotti" , "thread" , "Higher male voice" , "Male voice of high pitch, like Luciano" .)