Fiat is a noun that refers to a formal authorization or proposition. 

The Latin word feiri (fee AIR ee) mean’s ‘be done or made.’ By the Late Middle English period, fiat had become a word to describe a decree by a powerful leader. Example:

The principal didn’t care for the new school colors, so he had it changed by fiat. His choice of new colors were several times more atrocious, but no one dared challenge his rule.