Fiat \Fi"at\, n. [L., let it be done, 3d pers. sing., subj. pres., fr. fieri, used as pass. of facere to make. Cf. Be.]

1. An authoritative command or order to do something; an effectual decree.

His fiat laid the corner stone. --Willis.

2. (Eng. Law)
   (a) A warrant of a judge for certain processes.
   (b) An authority for certain proceedings given by the Lord Chancellor's signature.

Fiat money, irredeemable paper currency, not resting on a specie basis, but deriving its purchasing power from the declaratory fiat of the government issuing it.

Source: Webster's Revised Unabridged Dictionary (1913)