swamp poplar vs cottonwood

swamp poplar and cottonwood both are nouns.

Word	Noun	Adjective	Verb	Adverb
swamp poplar	Yes	No	No	No
cottonwood	Yes	No	No	No

As nouns, cottonwood is a hypernym of swamp poplar; that is, cottonwood is a word with a broader meaning than swamp poplar:

swamp poplar: North American poplar with large rounded scalloped leaves and brownish bark and wood
cottonwood: any of several North American trees of the genus Populus having a tuft of cottony hairs on the seed

swamp poplar (noun)	cottonwood (noun)
North American poplar with large rounded scalloped leaves and brownish bark and wood	any of several North American trees of the genus Populus having a tuft of cottony hairs on the seed
	American basswood of the Allegheny region