Crossword Genius

This is one party game (6)

Ross

I believe the answer is:

cluedo

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Here is my best explanation:

'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 is a kind of party).
'clue'+'do'='CLUEDO'

Ross

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

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