Folly

[fol-ee] /ˈfɒl i/

noun, plural follies for 2–6.
1.
the state or quality of being foolish; lack of understanding or sense.
2.
a foolish action, practice, idea, etc.; absurdity:
the folly of performing without a rehearsal.
3.
a costly and foolish undertaking; unwise investment or expenditure.
4.
Architecture. a whimsical or extravagant structure built to serve as a conversation piece, lend interest to a view, commemorate a person or event, etc.: found especially in England in the 18th century.
5.
follies, a theatrical revue.
6.
Obsolete. wickedness; wantonness.
/ˈfɒlɪ/
noun (pl) -lies
1.
the state or quality of being foolish; stupidity; rashness
2.
a foolish action, mistake, idea, etc
3.
a building in the form of a castle, temple, etc, built to satisfy a fancy or conceit, often of an eccentric kind
4.
(pl) (theatre) an elaborately costumed revue
5.
(archaic)

n.

early 13c., “mental weakness; unwise conduct” (in Middle English including wickedness, lewdness, madness), from Old French folie (12c.) “folly, madness, stupidity,” from fol (see fool (n.)). Sense of “costly structure considered to have shown folly in the builder” is attested from 1650s. Used since Middle English of place names, especially country estates, as a form of Old French folie in its meaning “delight.” Meaning “glamorous theatrical revue with lots of pretty girls” is from 1880, from French.