folly
UK[ˈfɒli]US[ˈfɑːli]
n
A foolish act, idea, or practice; lack of good sense or judgment.
n
A costly ornamental building with no practical purpose, especially a tower or mock-Gothic ruin, built in a large garden or park.
Etymology
The word 'folly' entered English in the early 13th century from Old French 'folie', meaning "madness, stupidity, or foolishness". This Old French term was itself derived from 'fol', meaning "mad, foolish", which can be traced back to Latin 'follis', meaning "bellows" or an "empty-headed person". The semantic evolution from "bellows" (something inflated with air) to "fool" is a classic metaphor for being "puffed up" with vanity or lacking substantive thought. By the mid-14th century, the architectural sense emerged, denoting an extravagant, whimsical structure that symbolized the owner's playful excess or "foolish" expenditure.
Analysis
The word 'folly' is a simplex word derived from Old French 'folie'. Its core morpheme is the entire word 'folly', which carries the meaning of "foolishness". It is not productively built from smaller, independent morphemes in modern English.
Examples
It would be sheer folly to ignore the expert advice.
The garden featured an elaborate 18th-century folly designed to look like a medieval castle.
His latest business venture proved to be an expensive folly.