American reluctant to pay for a bun? (8)

I believe the answer is:

tightwad

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'american' is the definition.
The answer and definition can be both people as well as being singular nouns.
Maybe you can see an association between them that I can't see?

I cannot understand how the remainder of the clue works.

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(Other definitions for tightwad that I've seen before include "Mean person (US)" , "Miser (sl.)" , "Skinflint" , "Miserly person" , "Cheapskate" .)

I've seen this clue in the Evening Standard.

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