SLAVON'IC, adjective [from Sclavi, a people of the north of Europe.] Pertaining to the Sclavi, a people that inhabited the country between the rivers Save and Drave, or to their language. Hence the word came to denote the language which is now spoken in Poland, Russia, Hungary, Bohemia, etc.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI