Most brisk in this Belfast establishment (7)

I believe the answer is:

fastest

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'most brisk' is the definition.
Both the answer and definition are superlative adjectives. Perhaps they are linked in a way I don't understand?

'in this belfast establishment' is the wordplay.
'in' indicates the answer is hidden within the clue.
'FASTEST' can be found hidden inside 'this belfast establishment'.

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(Other definitions for fastest that I've seen before include "Most rapid" , "Speediest" , "Quickest" , "Finishing first" .)

I've seen this clue in The Irish Times.

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