c. 1200, autorite, auctorite "authoritative passage or statement, book or quotation that settles an argument, passage from Scripture," from Old French autorité, auctorité "authority, prestige, right, permission, dignity, gravity; the Scriptures" (12c.; Modern French autorité), from Latin auctoritatem (nominative auctoritas) "invention, advice, opinion, influence, command," from auctor "master, leader, author" (see author (n.)). Usually spelled with a -c- in English before 16c., when the letter was dropped in imitation of French, then with a -th-, probably by influence of authentic.
From c. 1300 in the general sense "legal validity," also "authoritative book; authoritative doctrine" (opposed to reason or experience); "author whose statements are regarded as correct." From mid-14c. as "right to rule or command, power to enforce obedience, power or right to command or act." In Middle English also "power derived from good reputation; power to convince people, capacity for inspiring trust." From c. 1400 as "official sanction, authorization." Meaning "persons in authority" is from 1610s; Authorities "those in charge, those with police powers" is recorded from mid-19c.