Crossword Genius

Difficulty keeping pledge of secrecy about folly (7)

Ross

I believe the answer is:

madness

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'folly' is the definition.
(I know that folly can be written as madness)

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for madness that I've seen before include "Lunacy - ska/pop band" , "Folly" , "Utter foolishness" , "Insanity" , "fury" .)

I've seen this clue in The Daily Express.
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