Key to public property (6)
I believe the answer is:
estate
'property' is the definition.
(I know that property can be written as estate)
'key to public' is the wordplay.
'key' becomes 'e' (musical key).
'to public' becomes 'state' (similar in meaning).
'e'+'state'='ESTATE'
(Other definitions for estate that I've seen before include "The whole of a deceased person's assets" , "All that one owns at death" , "One's property after death" , "Possessions at the time of death" , "Housing area" .)