Longman Dictionary of Contemporary English - authority

~ n 1 »POWER« the power you have because of your official position or because people respect your knowledge and experience  (None of us questioned my father's authority. | the voice of authority (=a way of speaking that makes people respect you))  (Witten spoke with the voice of authority.) 2 the authorities the people or organizations that are in charge of a particular country or area  (British police are cooperating with the Malaysian authorities.) 3 »ORGANIZATION« an official organization or a local goverment department which controls public affairs, provides public services etc  (the Brewer Transit Authority | local authority)  (BrE)  (You can claim housing benefit from the local authority.) 4 I have it on good authority used to say that you are sure that something is true because you trust the person who told you about it 5 »EXPERT« someone who knows a lot about a subject and whose knowledge and opinions are greatly respected + on  (Professor Erikson is one of the world's leading authorities on tropical disease.) 6 »PERMISSION« official permission to do something  (Whose authority are you acting on?)