A party for John (5)

I believe the answer is:

privy

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'john' is the definition.
(synonyms)

I don't understand the remainder of the clue.

(Other definitions for privy that I've seen before include "Outside lavatory" , "John" , "Admitted (to secrets)" , "Hidden; outside toilet" , "bog" .)

I've seen this clue in The Sunday Times and The Times.

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