- the oldest attested Slavic language, an ecclesiastical language written first by Cyril and Methodius in a Bible translation of the 9th century and continued in use for about two centuries. It represents the South Slavic, Bulgarian dialect of 9th-century Salonika with considerable addition of other South and West Slavic elements. Abbreviation: OCS
- the oldest recorded Slavonic language: the form of Old Slavonic into which the Bible was translated in the ninth century, preserved as a liturgical language of various Orthodox Churches: belonging to the South Slavonic subbranch of languages
