Byelorussia vs Byelarus

Byelorussia and Byelarus both are nouns.

Word	Noun	Adjective	Verb	Adverb
Byelorussia	Yes	No	No	No
Byelarus	Yes	No	No	No

As nouns, Byelorussia and Byelarus are synonyms defined as:

Byelorussia and Byelarus: a landlocked republic in eastern Europe; formerly a European soviet

Other synonyms of Byelorussia include Belarus, Belorussia, Republic of Belarus, White Russia.

Byelorussia (noun)	Byelarus (noun)
a landlocked republic in eastern Europe; formerly a European soviet	a landlocked republic in eastern Europe; formerly a European soviet