Flexible bridge (6)

I believe the answer is:

rubber

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'flexible bridge' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's an association between them I don't understand?

This is the entire clue.

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(Other definitions for rubber that I've seen before include "Elastic material" , "Tree extract with erasing quality" , "Stationery item" , "Latex product" , "Stretchy substance" .)

I've seen this clue in The Mirror.

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