The phrase "an important authority" is correct and usable in written English.
It can be used when referring to a person or organization that has significant influence or expertise in a particular field or subject.
Example: "Dr. Smith is considered an important authority on climate change and environmental policy."
Alternatives: "a key expert" or "a significant figure".
"This is an important authority that we've been seeking for some time," Mr. Whitman said.
Though probably intended for the general reader, Mela's geography was cited by Pliny the Elder in his encyclopaedia of natural science as an important authority.
William Frederick Mangels (1867-1958) was a German immigrant, entrepreneur, and inventor, best known for his designs for mechanical amusements and carousels, and an important authority on the history of the amusements industry.
See Sally Beauty Co., 304 F.3d at 972; cf. King of the Mountain, 185 F.3d at 1089 ("Courts retain an important authority to monitor the outer limits of substantial similarity within which a jury is permitted to make the factual determination whether there is a likelihood of confusion". (brackets and internal quotation marks omitted)).
The Renaissance debate over the superiority of Aristotle or Galen was part of this rivalry: Aristotle was regarded by physicians as an important authority because of his philosophical system, but Galen had offered in his works more precise observations of the human body.
Others use the phrase "self-observing universe". It's startling when an important authority on the inflationary cosmos opens the door for human participation as a key element.
C. 150 İznik, Turkey 235 Dio Cassius, also spelled Dion Cassius or (in Byzantine sources) Dio Cocceianus, in full Lucius Cassius Dio (born c. 150, Nicaea, Bithynia [now İznik, Tur.] died 235) Roman administrator and historian, the author of Romaika, a history of Rome, written in Greek, that is a most important authority for the last years of the republic and the early empire.
Yasser Tabbaa, a specialist on Islamic art and architecture in Syria and Iraq, said of him, "He was a very important authority on possibly the most important archaeological site in Syria".
An especially important authority was Maximus Confessor, whose account of the return of all things Eriugena copiously borrowed.
This means that at least vis-à-vis arrest we found little support for the idea that those who use drugs are necessarily on a "bad course"—an important finding for both correctional authorities tasked with classifying and predicting people as likely recidivists, and for the classified-as-likely-recidivists themselves.
The House of Representives passed, H.R. 4310, the National Defense Authorization Act for Fiscal Year 2013, which includes provisions that would make NNSA a more autonomous agency, taking important authority away from DOE, and severely undermining nuclear security and safety.
