authority (n.) Look up authority at
early 13c., autorite "book or quotation that settles an argument," from Old French 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 till 16c., when it was dropped in imitation of the French. Meaning "power to enforce obedience" is from late 14c.; meaning "people in authority" is from 1610s. Authorities "those in charge, those with police powers" is recorded from mid-19c.