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

Even the creator of the Pet Rock — the preposterous 1975 phenomenon that was, yes, a rock in a box — tried to get in on the act. —ABC News, 13 June 2026

The idea of trying to fight inflation by slowing economic activity is preposterous. —Steve Forbes, Forbes.com, 12 June 2026

Which are totally preposterous. —Virginia Chamlee, PEOPLE, 12 June 2026

The series is wildly atmospheric with plenty of gallows humor and more than a few truly loopy plotlines, but great fun with Davis managing, as ever, to sell even the most preposterous scene. —Culture Critic, Los Angeles Times, 8 June 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.