The term fiat is from 1630s, "authoritative sanction," from Latin fiat "let it be done" (used in the opening of Medieval Latin proclamations and commands), third person singular present subjunctive of fieri "be done, become, come into existence" (from PIE root *bheue- "to be, exist, grow"), used as passive of facere "to make, do."
Fiat money is an intrinsically worthless object, such as paper money, that is deemed to be money by law. The use of fiat money became popular in the 20th century as governments and banks moved in to protect their economies from the frequent disruptions of the business cycle. The average life expectancy for a fiat currency is 27 years, with the shortest life span being one month. Founded in 1694, the British pound Sterling is the oldest fiat currency in existence, at 317 years old. Cryptocurrency is changing the game in fiat money.
Fiat existence, protect the experience, grow from the ashes