Preposterous means so absurd that it cannot be taken seriously. A preposterous claim, utterly preposterous, preposterous suggestion.
The Latin says it exactly: prae before plus posterus after, so a preposterous thing has the back part in front. It is a strong word and it dismisses rather than argues, which is why it works better in comedy than in a serious reply.
1adjectivepreposterousSo absurd that it cannot be taken seriously.
“His excuse that a dog had eaten his car keys was preposterous.”
preposterous is a quality of absurdity.
Latin praeposterus means with the hinder part in front — prae, before, plus posterus, coming after.
Latin
praeposterus — with the hinder part before, reversed, inverted, perverted
English, today
preposterous
Built from
From Latin praeposterus (“with the hinder part before, reversed, inverted, perverted”), from prae (“before”) + posterus (“coming after”).
Etymology from Wiktionary, CC BY-SA