Dunny cards (3)

I believe the answer is:

loo

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'dunny' is the definition.
Both the answer and definition are singular nouns.
Perhaps there's a link between them I don't understand?

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for loo that I've seen before include "Little boys' room" , "Lavatory - old card game" , "The little room - card game" , "WC - old card game" , "Card game; the 'smallest room'" .)

I've seen this clue in the Sydney Morning Herald.

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