Knock lazily but fast (7)

I believe the answer is:

rapidly

'fast' is the definition.
(synonyms)

'knock lazily' is the wordplay.
'knock' becomes 'rap' (synonyms).
'lazily' becomes 'idly' (synonyms).
'rap'+'idly'='RAPIDLY'

'but' is the link.

(Other definitions for rapidly that I've seen before include "Fast" , "Speedily" , "With great speed" , "At a great rate" , "Quickly" .)

I've seen this clue in the Evening Standard.

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