Slav vs European

Slav and European both are nouns.

Word	Noun	Adjective	Verb	Adverb
Slav	Yes	Yes	No	No
European	Yes	Yes	No	No

As nouns, European is a hypernym of Slav; that is, European is a word with a broader meaning than Slav:

Slav: any member of the people of eastern Europe or Asian Russia who speak a Slavonic language
European: a native or inhabitant of Europe

Other hypernyms of Slav include actor, doer, worker.

Slav (noun)	European (noun)
any member of the people of eastern Europe or Asian Russia who speak a Slavonic language	a native or inhabitant of Europe

Slav (adjective)	European (adjective)
speaking a Slavic language	of or relating to or characteristic of Europe or the people of Europe