He has to pay young lady, coming out with rock (6)
I believe the answer is:
debtor
'he has to pay' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'young lady coming out with rock' is the wordplay.
'young lady coming out' becomes 'deb' (I've seen this in another clue).
'with' is a charade indicator (letters next to each other).
'rock' becomes 'tor' (a tor is a rocky peak).
'deb'+'tor'='DEBTOR'
Can you help me to learn more?
(Other definitions for debtor that I've seen before include "Person owing money" , "Someone owing money" , "Person who owes money" , "One who owes money" , "Borrower" .)