The origin of the word fiat in English is connected to the origin of the world itself. Taken from the Latin meaning “let it be done,” this word appears in the Latin translation of Genesis, the first book of the bible, when God proclaimed “let there be light” (fiat lux). As a result, many early uses of fiat were biblical allusions, as in John Donne’s 1597 poem The Storm. In it he writes that there will be darkness unless “God say/Another Fiat.”
It was not until the 1630s that English speakers started using fiat to describe an “authoritative decree,” often issued by royalty or clergy—two groups that depended on divine right for their power. By the turn of the 19th century, English speakers applied fiat’s meaning to less-than-Godly legal manners. The phrase “fiat in bankruptcy” gained popularity at this time. Later that century, the concept of “fiat money,” or currency that has no intrinsic value, but that the government gives a value to by declaring it legal tender, took its place in English-speaking minds.
The name of Fiat, the Italian car company, is an acronym, not only a nod to this powerful word. Its name originally stood for Fabbrica Italiana Automobili Torino, meaning loosely “Italian automobile factory of Turin,” the region in which the country was founded.
According to the Google Ngram Viewer, the word “fiat” peaked in usage in the 1840s, possibly due to the political upheaval of the revolutions of 1848.
Fiat Lux: a Latin phrase which literally translates “let there be light” from Genesis 1:3.
Fiat: an Italian auto manufacturer, founded in 1899.
Fiat money: money that has value because the government says it has value.
“Ignoring an official fiat against the popular Rebel song ‘The Bonnie Blue Flag,’ Booth began to sing it in full voice one evening while walking down the street with several companions.”
—C. Brian Kelly, Ingrid Smyer-Kelly,
Best Little Ironies, Oddities, and Mysteries of the Civil War
“The despot ruled by fiat; if there were laws, they were given by him (or his predecessors) and he could withdraw or ignore them.”
—D. W. Treadgold,
The West in Russia and China, Volume 2