Money for a horse (6)
I believe the answer is:
amount
'money' is the definition.
The answer and definition can be both related to property as well as being singular nouns.
Maybe there's an association between them I don't understand?
'a horse' is the wordplay.
'horse' becomes 'mount' (mount is a kind of horse).
'a'+'mount'='AMOUNT'
'for' is the link.
Can you help me to learn more?
(Other definitions for amount that I've seen before include "Add up or be equivalent to" , "value" , "Size" , "Supply" , "Measure, quantity" .)