To dad, the old tax system (4)
I believe the answer is:
paye
'tax system' is the definition.
The answer and definition can be both related to property as well as being singular nouns.
Maybe you can see a link between them that I don't see?
'to dad the old' is the wordplay.
'to dad' becomes 'pa' (both can mean one's father).
'the old' becomes 'ye' (resembles a historical spelling of 'the').
'pa'+'ye'='PAYE'
Can you help me to learn more?
(Other definitions for paye that I've seen before include "The working persons' tax system" , "System of withholding tax" , "The tax system for the working man" , "Plain man's income tax system" , "Tax system for Joe Soap" .)