Sides with country cousin out of the capital (4)

I believe the answer is:

coin

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'capital' is the definition.
The definition and answer can be both related to property as well as being singular nouns.
Perhaps you can see an association between them that I don't see?

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for coin that I've seen before include "Penny, say?" , "Metallic money" , "Invent (a new word)" , "Metal money disc" , "Metal used as money" .)

I've seen this clue in the Irish Times (Crosaire) and the Irish Times.

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