The Spanish word 'fíat' comes directly from the Latin word 'fiat', which means 'let it be done'. This Latin word was the third-person singular present subjunctive of the verb 'fieri' (to become, to be done). In Spanish, 'fíat' evolved to mean 'authorization' or 'consent', maintaining a connection to its original meaning of giving permission for something to be done.

While 'fíat' is relatively uncommon in Spanish, it doesn't have many closely related simpler Spanish words. However, you might encounter it in formal or legal contexts where it refers to an official authorization or decree.

The English language also borrowed the Latin word 'fiat' directly, where it means 'an authoritative decree, sanction, or order'. You might be familiar with the phrase 'fiat currency', which refers to money that has value because of government decree rather than being backed by a commodity. The car company FIAT also takes its name from this Latin word - it was originally an acronym that included this Latin word, meaning 'let it be done'.