/fee"aht, -at; fuy"euht, -at/ , 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.
[ 1625-35; fieri to become ]