Pronunciation: (fē'ät, -at; fī'ut, -at),[key] —n. 1. an authoritative decree, sanction, or order: a royal fiat. 2. a formula containing the word fiat, by which a person in authority gives sanction.
3. an arbitrary decree or pronouncement, esp. by a person or group of persons having absolute authority to enforce it: The king ruled by fiat.