Noun

(label) The power to enforce rules or give orders.

* 1883 , (Howard Pyle), (The Merry Adventures of Robin Hood)

But in the meantime Robin Hood and his band lived quietly in Sherwood Forest, without showing their faces abroad, for Robin knew that it would not be wise for him to be seen in the neighborhood of Nottingham, those in authority being very wroth with him.

(label) Persons in command; specifically, government.

*{{quote-book, year=1927, author= F. E. Penny

, chapter=4, title= Pulling the Strings , passage=The case was that of a murder. It had an element of mystery about it, however, which was puzzling the authorities . A turban and loincloth soaked in blood had been found; also a staff.}}

* {{quote-magazine, date=2013-08-10, volume=408, issue=8848, magazine=(The Economist)

, title= Legal highs: A new prescription , passage=No sooner has a [synthetic] drug been blacklisted than chemists adjust their recipe and start churning out a subtly different one. These “legal highs” are sold for the few months it takes the authorities to identify and ban them, and then the cycle begins again.}}

(label) A person accepted as a source of reliable information on a subject.

* 1930 September 18, Albert Einstein, as quoted in Albert Einstein: Creator and Rebel (1988) by Banesh Hoffman

To punish me for my contempt of authority', Fate has made me an ' authority myself.

Noun

(wikipedia expertise) (-)

Great skill or knowledge in a particular field or hobby

The scientist has expertise in the field of nuclear fusion.

* 2014 , Michael White, " Roll up, roll up! The Amazing Salmond will show a Scotland you won't believe", The Guardian , 8 September 2014:

He spoke of Scotland's hydroelectric projects in Africa, local expertise shared with the world's poor.

advice, or opinion, of an expert