This is one party game (6)

I believe the answer is:

cluedo

'game' is the definition.
(I've seen this before)

'this is one party' is the wordplay.
'this is one' becomes 'clue' (this clue).
'party' becomes 'do' (do can informally mean a party).
'clue'+'do'='CLUEDO'

(Other definitions for cluedo that I've seen before include "Detective game" , "Murder mystery board game" .)

I've seen this clue in The Guardian.

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