Old Church Slavonic or Old Slavonic () is the first Slavic literary language.
Historians credit the 9th-century Byzantine missionaries Saints Cyril and Methodius with standardizing the language and undertaking the task of translating the Gospels and necessary liturgical books into it as part of the Christianization of the Slavs. It is thought to have been based primarily on the dialect of the 9th-century Byzantine Slavs living in the Province of Thessalonica (in present-day Greece).
Old Church Slavonic played an important role in the history of the Slavic languages and served as a basis and model for later Church Slavonic traditions, and some Eastern Orthodox and Eastern Catholic churches use this later Church Slavonic as a liturgical language to this day.
As the oldest attested Slavic language, OCS provides important evidence for the features of Proto-Slavic, the reconstructed common ancestor of all Slavic languages.
Nomenclature
The name of the language in Old Church Slavonic texts was simply Slavic (словѣ́ньскъ ѩꙁꙑ́къ, slověnĭskŭ językŭ), derived from the word for Slavs (словѣ́нє, slověne), the self-designation of the compilers of the texts. This name is preserved in the modern native names of the Slovak and Slovene languages. The language is sometimes called Old Slavic, which may be confused with the distinct Proto-Slavic language. Different strains of nationalists have tried to 'claim' Old Church Slavonic; thus OCS has also been variously called Old Bulgarian, Old Croatian, Old Macedonian or Old Serbian, or even Old Slovak, Old Slovenian. The commonly accepted terms in modern English-language Slavic studies are Old Church Slavonic and Old Church Slavic.
The term Old Bulgarian (, ) is the only designation used by Bulgarian-language writers. It was used in numerous 19th-century sources, e.g. by August Schleicher, Martin Hattala, Leopold Geitler and August Leskien, who noted similarities between the first literary Slavic works and the modern Bulgarian language. For similar reasons, Russian linguist Aleksandr Vostokov used the term Slav-Bulgarian. The term is still used by some writers but nowadays normally avoided in favor of Old Church Slavonic.
The term Old Macedonian is occasionally used by Western scholars in a regional context.
The obsolete term Old Slovenian was used by early 19th-century scholars who conjectured that the language was based on the dialect of Pannonia.
History
Byzantine missionaries standardized the language for the expedition of the two apostles, Cyril and his brother Methodius, to Great Moravia (the territory of today's eastern Czechia and western Slovakia; see Glagolitic alphabet for details). For that purpose, Cyril and Methodius started to translate religious literature into Old Church Slavonic, allegedly basing the language on the Slavic dialect spoken in the hinterland of their hometown, Thessaloniki, in present-day Greece.
Based on a number of archaicisms preserved until the early 20th century (the articulation of yat as in Boboshticë, Drenovë, around Thessaloniki, Razlog, the Rhodopes and Thrace and of yery as around Castoria and the Rhodopes, the presence of decomposed nasalisms around Castoria and Thessaloniki, etc.), the dialect is posited to have been part of a macrodialect extending from the Adriatic to the Black sea, and covering southern Albania, northern Greece and the southernmost parts of Bulgaria.
As part of preparations for the mission, in 862/863, the Glagolitic alphabet was developed and the most important prayers and liturgical books, including the Aprakos Evangeliar (a Gospel Book lectionary containing only feast-day and Sunday readings), the Psalter, and the Acts of the Apostles, were translated. (The Gospels were also translated early, but it is unclear whether Cyril or Methodius had a hand in this.)
The language and the Glagolitic alphabet, as taught at the Great Moravian Academy (), were used for government and religious documents and books between 863 and 885. The texts written during this phase contain characteristics of the West Slavic vernaculars in Great Moravia.
In 885 Pope Stephen V prohibited the use of Old Church Slavonic in Great Moravia in favour of Latin. King Svatopluk I of Great Moravia expelled the Byzantine missionary contingent in 886.