A foolish construction (5)
I believe the answer is:
folly
'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.
Can you help me to learn more?
(Other definitions for folly that I've seen before include "Absurdity" , "Lunacy" , "'Madness, stupidity (5)'" , "Foolish thing" , "mock Gothic building" .)