Americanism vs usage

Americanism and usage both are nouns.

Word	Noun	Adjective	Verb	Adverb
Americanism	Yes	No	No	No
usage	Yes	No	No	No

As nouns, usage is a hypernym of Americanism; that is, usage is a word with a broader meaning than Americanism:

Other hypernyms of Americanism include custom, usance.

Americanism (noun)	usage (noun)
a custom that is peculiar to the United States or its citizens	the act of using
loyalty to the United States and its institutions	accepted or habitual practice
an expression that is characteristic of English as spoken by Americans	the customary manner in which a language (or a form of a language) is spoken or written