From the sound of it, any entering upset tiny number! (6)

I believe the answer is:

ninety

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'number' is the definition.
(ninety is a kind of whole number)

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

(Other definitions for ninety that I've seen before include "Figure in inn, yet, strangely" , "Fourscore and ten" , "Excellent percentage score" , "old age" , "XC (in ancient Rome)" .)

I've seen this clue in the Sydney Morning Herald.

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