Foolishness
Part of speech: noun
Definition: The state of being foolish. A thing or event that is foolish, or an absurdity.
Example sentence: Almost all new ideas have a certain aspect of foolishness when they are first produced.
Folly
Part of speech: noun
Definition: foolishnessthoughtless action resulting in tragic consequencea fanciful building built for purely ornamental reasons
Example sentence: The folly of mistaking a paradox for a discovery, a metaphor for a proof, a torrent of verbiage for a spring of capital truths, and oneself for an oracle, is inborn in us.