Decidedly 2-D (6)

I believe the answer is:

deuced

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'decidedly' is the definition.
Both the definition and answer are adverbs. Maybe you can see an association between them that I can't see?

'2-d' is the wordplay.
'2' becomes 'deuce' (synonyms).
'deuce'+'d'='DEUCED'

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I've seen this clue in The Guardian.

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