noun
An arbitrary or authoritative command or order to do something; an effectual decree.
Authorization, permission or (official) sanction.
(English law) A warrant of a judge for certain processes.
(English law) An authority for certain proceedings given by the Lord Chancellor's signature.
(attributive) (Pertaining to) fiat currency.
verb
(transitive, used in academic debate and role-playing games) To make (something) happen.
(transitive, law) To issue a fiat.