fi ‧ at /ˈfiːæt, ˈfaɪæt/ BrE AmE noun [countable] formal
[ Date: 1300-1400 ; Language: Latin ; Origin: 'let it be done' , from fieri 'to become, be done' ]
an official order given by someone in a position of authority, without considering what other people want
by fiat
The matter was settled by presidential fiat.