Penthouses may supply money for Bill (7)
I believe the answer is:
payment
'penthouses may' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'money for bill' is the wordplay.
'money' becomes 'pay' (I've seen this in other clues).
'for bill' becomes 'ment' (I can't justify this - if you can you should give a lot more credence to this answer).
'pay'+'ment'='PAYMENT'
'supply' is the link.
Can you help me to learn more?
(Other definitions for payment that I've seen before include "Money given for service etc." , "Discharge of an obligation with money" , "Handing over money" , "Settlement, remittance" , "Punishment" .)