preposterous

adjective

pre·​pos·​ter·​ous pri-ˈpä-st(ə-)rəs 

: contrary to nature, reason, or common sense : absurd

The whole idea is preposterous!

preposterously adverb

preposterousness noun

Synonyms of preposterous

• absurd
• bizarre
• foolish
• unreal
• insane

Examples of preposterous in a Sentence

The whole idea is preposterous!

the idea that extraterrestrials built the pyramids is preposterous

Recent Examples on the Web

Tasked only with scoring, the 5-foot-11 Long Rife put up truly preposterous numbers at Union-Whitten High School. —Joseph Dycus, Mercury News, 28 Mar. 2026

One Boston city council member, Julia Mejia, is pushing a home rule petition allowing non-citizens to vote in elections, a preposterous prospect that is making the city a laughingstock. —Joe Battenfeld, Boston Herald, 26 Mar. 2026

Which makes the city's lack of the viral soft serve margaritas feel preposterous. —Eddie Fontanez, AZCentral.com, 26 Mar. 2026

Using a premise inspired by Eternal Sunshine of the Spotless Mind and Waking Life–like rotoscope animation, the concept is grounded enough to explore the desperate people using fringe science to fix their lives while also having a sense of humor about how preposterous human fears and desires are. —Eric Vilas-Boas, Vulture, 18 Mar. 2026

Word History

Etymology

Latin praeposterus, literally, in the wrong order, from prae- + posterus hinder, following — more at posterior

First Known Use

1533, in the meaning defined above

Kids Definition

preposterous

adjective

pre·​pos·​ter·​ous pri-ˈpäs-t(ə-)rəs 

: making little or no sense : absurd

preposterously adverb

preposterousness noun

Etymology

from Latin praeposterus, literally, "having the rear part in front," from prae- "in front, before" and posterus "coming behind, following"

Word Origin

The familiar expression "putting the cart before the horse" comes very close to the literal sense of the word preposterous. The Romans formed their Latin adjective praeposterus from prae-, meaning "before," and posterus, meaning "following." They at first used it to mean "having that first which ought to be last," like having a cart ahead of the horse that is pulling it. Praeposterus was used to describe something that was out of the normal or logical order or position. From this developed the more general sense of "ridiculous, absurd." These meanings were borrowed into English in the 16th century. Although preposterous is seldom used in its literal sense nowadays, we still use it to describe something that seems so unreasonable as to be ridiculous.