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. Abbr.: OCS Also called Old' Church' Slav'ic, Old Slavic, Old Slavonic. Cf. Church Slavic.