Became smaller when ironed? (9)

I believe the answer is:

decreased

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'ironed?' is the definition.
(I've seen this in another clue)

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

(Other definitions for decreased that I've seen before include "Became smaller or fewer" , "Dropped" , "contracted" .)

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

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