Injun vs Amerindian

Injun and Amerindian both are nouns.

Word	Noun	Adjective	Verb	Adverb
Injun	Yes	No	No	No
Amerindian	Yes	No	No	No

As nouns, Amerindian is a hypernym of Injun; that is, Amerindian is a word with a broader meaning than Injun:

Injun: (slang) offensive term for Native Americans
Amerindian: any member of the peoples living in North or South America before the Europeans arrived

Other hypernyms of Injun include Native American.

Injun (noun)	Amerindian (noun)
(slang) offensive term for Native Americans	any member of the peoples living in North or South America before the Europeans arrived