(of a person, institution, or written work) The quality or characteristic of being respected for having good character or knowledge, especially as a source of guidance or an exemplar of proper conduct.

Any authority which has a legal mandate to govern, administrate a part or aspect of public life, such as all branches of the executive power of a state, province, municipality etc.

(rhetoric) Deeming an assertion to be true because of the position or the authority of the person asserting it.

(Australia, New Zealand, UK, law) A body set up by law which is authorised to enforce legislation on behalf of the relevant country or state.

A government organization responsible for collecting taxes.

plural of appeal to authority

A public authority which operates a port or other transportation infrastructure.

In local government, a single-tier authority which replaces a two-tier structure. For example, in England, county councils are abolished and their responsibilities are transferred to boroughs and local government districts (but this only applies to some counties, not all). In some cases complete counties, such as Cornwall and Northumberland, are now unitary authorities without any subdivision into local government districts.

Someone who is in a position of authority.

(library science) The organization of bibliographic information by using a single distinct spelling of a name (heading) or a numeric identifier for each topic or agent.