Knyaz or knez is a historical Slavic title, used both as a royal and noble title in different times of history and different ancient Slavic lands. It is usually translated into English as prince, duke or count, depending on specific historical context and the potentially known Latin equivalents of the title for each bearer of the name. In Latin, sources the title is usually translated as comes or princeps, but the word was originally derived from the Proto-Germanic kuningaz (king).
The female form transliterated from Bulgarian and Russian is knyaginya (княгиня), kniahynia (княгиня) in Ukrainian, kneginja in Slovene, Croatian and Serbian (Serbian Cyrillic: кнегиња). In Russian, the daughter of a knyaz is knyazhna (княжна), in Ukrainian is kniazivna (князівна). In Russian, the son of a knyaz is knyazhich (княжич) (old form).
The title is pronounced and written similarly in different European languages. In Croatian, Bosnian and West Slavic languages, such as Polish, the word has later come to denote "lord", and in Czech, Polish and Slovak also came to mean "priest" (kněz, ksiądz, kňaz) as well as "duke" (knez, kníže, książę, knieža). In Sorbian it means simply "Mister" (from "Master". Cf French "monsieur" from "mon sieur" "my lord"). Today the term knez is still used as the most common translation of "prince" in Bosnian, Croatian and Serbian literature. "Knez" is also found as a surname in former Yugoslavia.
The etymology is ultimately a cognate of the English king, the German König, and the Swedish konung. The proto-Slavic form was кънѧѕь kŭnędzĭ, Church Slavonic: кънѧѕь kŭnędzĭ, Bulgarian: княз, Old East Slavic: князь knyazĭ, Polish: książę, Bosnian and Serbian: kнез, Bosnian, Croatian, Serbian, and Slovene: knez, Czech: kníže etc., as it could be a very early borrowing from the already extinct Proto-Germanic Kuningaz, a form also borrowed by Finnish and Estonian (Kuningas).
The meaning of the term changed over the course of history. Initially the term was used to denote the chieftain of a tribe. Later, with the development of feudal statehood, it became the title of a ruler of a state, and among East Slavs (Russian: княжество (kniazhestvo), Ukrainian: князівство (knyazivstvo) traditionally translated as duchy or principality), for example, of Kievan Rus'. In medieval Latin sources the title was rendered as either rex or dux.
In Bulgaria, Simeon took the title of tsar in 913. In Kievan Rus', as the degree of centralization grew, the ruler acquired the title Velikii Knyaz (Великий Князь) (translated as Grand Prince or Grand Duke, see Russian Grand Dukes). He ruled a Velyke Knyazivstvo (Велике Князiвcтво) (Grand Duchy), while a ruler of its vassal constituent (udel, udelnoe knyazivstvo or volost) was called udelny knyaz or simply knyaz.
When Kievan Rus' became fragmented in the 13th century, the title Kniaz continued to be used in East Slavic states, including Kiev, Chernigov, Novgorod, Pereiaslav, Vladimir-Suzdal', Muscovy, Tver, Halych-Volynia, and in the Grand Duchy of Lithuania.
As noted above, the title knyaz or kniaz became a hereditary noble title in the Grand Duchy of Moscow and the Grand Duchy of Lithuania. Following the union of the Kingdom of Poland and the Grand Duchy of Lithuania, kniaź became a recognised title in the Polish-Lithuanian Commonwealth. By the 1630s - apart from the title pan, which indicated membership of the large szlachta noble class - kniaź was the only hereditary title that was officially recognised and officially used in the Polish-Lithuanian Commonwealth. Notable holders of the title kniaź include Jeremi Wiśniowiecki.
As the Tsardom of Russia gained dominion over much of former Kievan Rus', Velikii Kniaz (Great Kniaz) Ivan IV of Russia in 1547 was crowned as Tsar. From the mid-18th century onwards, the title Velikii Kniaz was revived to refer to (male-line) sons and grandsons of Russian Emperors. See titles for Tsar's family for details.
Kniaz (Russian: Кня́зь, IPA: [ˈknʲæsʲ]) continued as a hereditary title of Russian nobility patrilineally descended from Rurik (e.g., Belozersky, Belosselsky-Belozersky, Repnin, Gorchakov) or Gediminas (e.g., Galitzine, Troubetzkoy). Members of Rurikid or Gedyminid families were called princes when they ruled tiny quasi-sovereign medieval principalities. After their demesnes were absorbed by Muscovy, they settled at the Moscow court and were authorised to continue with their princely titles.
From the 18th century onwards, the title was occasionally granted by the Tsar, for the first time by Peter the Great to his associate Alexander Menshikov, and then by Catherine the Great to her lover Grigory Potemkin. After 1801, with the incorporation of Georgia into the Russian Empire, various titles of numerous local nobles were controversially rendered in Russian as "kniazes". Similarly, many petty Tatar nobles asserted their right to style themselves "kniazes" because they descended from Genghis Khan.
See also "Velikiy Knyaz" article for more details.
Finally, within the Russian Empire of 1809-1917, Finland was officially called Grand Principality of Finland (fi Suomen suuriruhtinaskunta, sv Storfurstendömet Finland, ru Velikoye Knyazhestvo Finlyandskoye).
In the 19th century, the Serbian term knez (кнез) and the Bulgarian term knyaz (княз) were revived to denote semi-independent rulers of those countries, such as Alexander Karađorđević and Alexander of Battenberg. In parts of Serbia and western Bulgaria, knez was the informal title of the elder or mayor of a village or zadruga until around the 19th century. Those are officially called градоначелник (gradonačelnik) (Serbia) and градоначалник (gradonachalnik) or кмет (kmet) (Bulgaria).