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[fee-aht, -at; fahy-uh t, -at] /ˈfi ɑt, -æt; ˈfaɪ ət, -æt/
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.
Origin of fiat
1625-35; < Latin: let it be done, 3rd singular present subjunctive of fierī to become

fiat justitia, ruat caelum

[fee-aht yoo s-tee-tee-ah roo-aht kahy-loo m; English fee-aht juhs-tish-ee-uh roo-at see-luh m, fahy-uh t] /ˈfi ɑt yʊsˈti tiˌɑ ˈru ɑt ˈkaɪ lʊm; English ˈfi ɑt dʒʌsˈtɪʃ i ə ˈru æt ˈsi ləm, ˈfaɪ ət/
let there be justice though the heavens fall.

fiat lux

[fee-aht loo ks; English fee-aht luhks, fahy-uh t] /ˈfi ɑt ˈlʊks; English ˈfi ɑt ˈlʌks, ˈfaɪ ət/
let there be light. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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Examples from the Web for fiat
Contemporary Examples
Historical Examples
  • fiat—8-cylinder, air-cooled; 50 horse power; weight 150 pounds.

    Flying Machines W.J. Jackman and Thos. H. Russell
  • The fiat demanded no limitation to her stay with “sister” Emma.

    The Hound From The North Ridgwell Cullum
  • He had to meet the tired, sweet servitors without and announce a man's fiat.

    The Prisoner Alice Brown
  • fiat voluntas &c. thy will be done in earth as it is in heuen.

  • He became the umpire of taste, and his word was received as the fiat of fashion.

    Evenings at Donaldson Manor Maria J. McIntosh
British Dictionary definitions for fiat


/ˈfaɪət; -æt/
official sanction; authoritative permission
an arbitrary order or decree
(mainly literary) any command, decision, or act of will that brings something about
Word Origin
C17: from Latin, literally: let it be done, from fierī to become
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for fiat

"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.

Online Etymology Dictionary, © 2010 Douglas Harper
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