authority

An authority is a public organization that controls an area or certain activities. (noun)

A corporation that provides bus service in a city is an example of a transit authority.

An authority is a person who is considered an expert in his field. (noun)

A philosophy scholar who publishes books is an example of an authority.

See authority in Webster's New World College Dictionary

1. the power or right to give commands, enforce obedience, take action, or make final decisions; jurisdiction
2. the position of one having such power: a person in authority
such power as delegated to another; authorization; warrant: he has my authority to do it
power or influence resulting from knowledge, prestige, etc.
1. the citation of a writing, decision, etc. in support of an opinion, action, etc.
2. the writing, etc. cited
reliability of a source or witness
1. persons, esp. in government, having the power or right to enforce orders, laws, etc.
2. a government agency that administers a project
a person with much knowledge or experience in some field, whose information or opinion is hence reliable; expert
self-assurance and expertness that come with experience: the pianist's performance lacked authority

See authority in American Heritage Dictionary 4

(ə-thôrˈĭ-tē, ə-thŏrˈ-, ô-thôrˈ-, ô-thŏrˈ-)

noun pl. au·thor·i·ties

a. The power to enforce laws, exact obedience, command, determine, or judge.
b. One that is invested with this power, especially a government or body of government officials: land titles issued by the civil authority.
Power assigned to another; authorization: Deputies were given authority to make arrests.
A public agency or corporation with administrative powers in a specified field: a city transit authority.
a. An accepted source of expert information or advice: a noted authority on birds; a reference book often cited as an authority.
b. A quotation or citation from such a source: biblical authorities for a moral argument.
Justification; grounds: On what authority do you make such a claim?
A conclusive statement or decision that may be taken as a guide or precedent.
Power to influence or persuade resulting from knowledge or experience: political observers who acquire authority with age.
Confidence derived from experience or practice; firm self-assurance: played the sonata with authority.