Muso bishop associates with Help! (7)
I believe the answer is:
bassist
'muso' is the definition.
Both the answer and definition are singular nouns.
Perhaps you can see an association between them that I can't see?
'bishop associates with help' is the wordplay.
'bishop' becomes 'B' (abbreviation for bishop in chess).
'associates with' says to put letters next to each other.
'help' becomes 'assist' (to assist someone is to help them).
'b'+'assist'='BASSIST'
Can you help me to learn more?
(Other definitions for bassist that I've seen before include "jazz player" , "Musician" .)