Nahuatl vs Amerindian

Nahuatl and Amerindian both are nouns.

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

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

Nahuatl: a member of any of various Indian peoples of central Mexico
Amerindian: any member of the peoples living in North or South America before the Europeans arrived

Other hypernyms of Nahuatl include Native American.

Nahuatl (noun)	Amerindian (noun)
the Uto-Aztecan language spoken by the Nahuatl	any member of the peoples living in North or South America before the Europeans arrived
a member of any of various Indian peoples of central Mexico