(1):

(n.) Legal or rightful power; a right to command or to act; power exercised buy a person in virtue of his office or trust; dominion; jurisdiction; authorization; as, the authority of a prince over subjects, and of parents over children; the authority of a court.

(2):

(n.) Government; the persons or the body exercising power or command; as, the local authorities of the States; the military authorities.

(3):

(n.) The power derived from opinion, respect, or esteem; influence of character, office, or station, or mental or moral superiority, and the like; claim to be believed or obeyed; as, an historian of no authority; a magistrate of great authority.

(4):

(n.) That which, or one who, is claimed or appealed to in support of opinions, actions, measures, etc.

(5):

(n.) Testimony; witness.

(6):

(n.) A precedent; a decision of a court, an official declaration, or an opinion, saying, or statement worthy to be taken as a precedent.

(7):

(n.) A book containing such a statement or opinion, or the author of the book.

(8):

(n.) Justification; warrant.