Run of the mill currency (4)

I believe the answer is:

race

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'run' is the definition.
(I know that run can be written as race)

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

(Other definitions for race that I've seen before include "Move fast" , "Run fast" , "Speed competition" , "Contest; nation" , "eg The Oaks" .)

I've seen this clue in The Globe and Mail.

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