say it: FAH-lee
folly is a noun meaning "the trait of acting stupidly or rashly". It carries 4 recorded senses.
the trait of acting stupidly or rashly
a stupid mistake
the quality of being rash and foolish
“trying to drive through a blizzard is the height of folly”
“adjusting to an insane society is total foolishness”
foolish or senseless behavior
Forms marked · are formed by the regular rule rather than recorded in the source data. English keeps a few hundred irregulars and the rest follow the pattern, so the rule is right far more often than not — but it is a rule, and the mark says so.
Definitions, synonyms and semantic relations for folly come from Princeton University’s WordNet. The pronunciation comes from the CMU Pronouncing Dictionary. Commonness is measured against a corpus of everyday English. Full sources and licences.