In bar, everyone passed back 8 nickels (6)

I believe the answer is:

dollar

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'in' is the definition.
The answer and definition can be both quantities as well as being singular nouns.
Maybe they are linked in a way I don't understand?

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for dollar that I've seen before include "American currency" , "One hundred cents" , "100 cents" , "Australian currency" , "Foreign currency" .)

I've seen this clue in The Telegraph.

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