- an authoritative decree, sanction, or order: a royal fiat.
- a fixed form of words containing the word fiat, by which a person in authority gives sanction, or authorization.
- an arbitrary decree or pronouncement, especially by a person or group of persons having absolute authority to enforce it: The king ruled by fiat.
- let there be justice though the heavens fall.
- let there be light.
- official sanction; authoritative permission
- an arbitrary order or decree
- mainly literary any command, decision, or act of will that brings something about
“authoritative sanction,” 1630s, from Latin fiat “let it be done” (also used in the opening of Medieval Latin proclamations and commands), third person singular present subjunctive of fieri, used as passive of facere “to make, do” (see factitious). Also sometimes a reference to fiat lux “let there be light” in the Book of Genesis.