Number often reduced (3)

I believe the answer is:

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'number' is the definition.
(I know that ten is a type of large integer)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for ten that I've seen before include "How many" , "Dudley Moore/Bo Derek film" , "honour" , "X-WORD" , "PM's address, Downing St" .)

I've seen this clue in the Evening Standard.

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