A foolish construction (5)

I believe the answer is:

folly

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'a foolish construction' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Maybe they are linked in a way I don't understand?

This is all the clue.

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(Other definitions for folly that I've seen before include "Absurdity" , "Lunacy" , "'Madness, stupidity (5)'" , "Foolish thing" , "mock Gothic building" .)

I've seen this clue in the Evening Standard.

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