Tokyo vs Tokio

Tokyo and Tokio both are nouns.

Word	Noun	Adjective	Verb	Adverb
Tokyo	Yes	No	No	No
Tokio	Yes	No	No	No

As nouns, Tokyo and Tokio are synonyms defined as:

Tokyo and Tokio: the capital and largest city of Japan; the economic and cultural center of Japan

Other synonyms of Tokyo include capital of Japan, Edo, Japanese capital, Yeddo, Yedo.

Tokyo (noun)	Tokio (noun)
the capital and largest city of Japan; the economic and cultural center of Japan	the capital and largest city of Japan; the economic and cultural center of Japan