authority is the power or right to give commands, enforce obedience, and make binding decisions — and, in a separate sense, a person or source whose standing makes their statements accepted as settled.
The two senses pull in different directions and the word carries both without strain. Positional authority is conferred: a judge, a licensing board, or a port authority holds it because a structure grants it, and the plural the authorities names the officials who exercise it, a usage established by the mid-nineteenth century. Epistemic authority is earned: someone is an authority on a subject because their work compels assent, and a text cited to settle a dispute is likewise called an authority. The distinction matters because the second kind cannot be issued and the first kind cannot be studied into existence.
Political theory separates authority from raw power by legitimacy — whether those subject to it accept its validity rather than merely submitting to force. Max Weber's standard typology names three sources of that legitimacy: traditional, resting on inherited custom; charismatic, resting on the personal pull of a leader; and legal-rational, resting on impersonal rules and offices. Authority in this sense is adjacent to 📝influence but not identical to it: influence changes what someone wants to do, while authority changes what they are obliged to do.
The word entered English around 1200 from Old French autorité, from Latin auctoritatem, from auctor, "master, originator, author" — so authority and author are the same word twice, both naming the one who originates and is therefore answerable for what follows. Early English spelled it with a -c-, dropped that in imitation of French, and acquired the -th- in the early fifteenth century, probably by analogy with authentic.