An example of a preposterous idea is that the world is flat.
Origin of preposterous
- From Latin praeposterus inverted, unseasonable prae- pre- posterus coming behind (from post behind apo- in Indo-European roots)
From American Heritage Dictionary of the English Language, 5th Edition
- From Latin praeposterus (“with the hinder part before, reversed, inverted, perverted"), from prae (“before") + posterus (“coming after").