At bottom, you can bet it with confidence (6)

I believe the answer is:

dollar

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'at' 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 can't explain the rest of the clue.

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(Other definitions for dollar that I've seen before include "US currency" , "100 cents" , "American's ready" , "Standard monetary unit of many countries" , "Foreign currency" .)

I've seen this clue in the Evening Standard.

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