American smelt vs rainbow smelt

American smelt and rainbow smelt both are nouns.

Word	Noun	Adjective	Verb	Adverb
American smelt	Yes	No	No	No
rainbow smelt	Yes	No	No	No

As nouns, American smelt and rainbow smelt are synonyms defined as:

American smelt and rainbow smelt: common smelt of eastern North America and Alaska

American smelt (noun)	rainbow smelt (noun)
common smelt of eastern North America and Alaska	important marine and landlocked food fish of eastern North America and Alaska
	common smelt of eastern North America and Alaska