Unearned income? (6,3)
I believe the answer is:
strike pay
'unearned income?' is the definition.
The answer and definition can be both related to property as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
This is the entire clue.
Can you help me to learn more?
(Other definitions for strike pay that I've seen before include "it's paid to those not acting?" , "Money for those taking industrial action" .)