A roll or bun (3)

I believe the answer is:

wad

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'a roll' is the definition.
(roll of banknotes)

I don't understand the remainder of the clue.

(Other definitions for wad that I've seen before include "Bankroll; sandwich (slang)" , "Small mass of soft material" , "Small bundle" , "Bundle of soft material or of banknotes" , "Compact mass" .)

I've seen this clue in the Evening Standard.

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