Crossword Genius

Eastern bread — you must bin old one (4)

Ross

I believe the answer is:

yuan

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'one' is the definition.
The definition and answer can be both quantities as well as being singular nouns.
Maybe you can see a link between them that I don't see?

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for yuan that I've seen before include "Income in Shanghai" , "Chinese monetary unit" , "Monetary unit of China" , "money abroad" , "foreign currency" .)

I've seen this clue in The Times and The Sunday Times.
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