Ten inflated and deflated (9)

I believe the answer is:

flattened

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'ten' is the definition.
Both the definition and answer are adjectives. Perhaps you can see an association between them that I can't see?

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for flattened that I've seen before include "Pressed, rolled out" , "Made level and even" , "Compressed" , "Squashed" .)

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

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