(historical) An ancient city in Bithynia in Asia Minor, important during Roman and Byzantine times, on the site of modern-day İznik, Turkey, to which it gave its name. Famous as the site of the First Council of Nicaea in 325 AD, which composed the Nicene Creed.

plural of Nicaean

Of or relating to Nicaea. / Of or relating to the Empire of Nicaea, a medieval polity centred on the city.

A person from Nicaea or the Empire of Nicaea. / A person who supports the Nicene Creed.