Church Slavonic Definition

noun

Webster's New World

Any of the forms of Old Church Slavonic that are used as liturgical languages in Slavic-speaking Eastern Orthodox and Eastern Catholic churches and that are influenced in pronunciation and grammar by the local Slavic language spoken by the church communities.

American Heritage

pronoun

A liturgical language of various Slavic church traditions, with dialectal basis of Old Church Slavonic mixed with vernacular lexical and phonological developments.

Wiktionary