cotton thistle vs Onopordum acanthium

cotton thistle and Onopordum acanthium both are nouns.

Word	Noun	Adjective	Verb	Adverb
cotton thistle	Yes	No	No	No
Onopordum acanthium	Yes	No	No	No

As nouns, cotton thistle and Onopordum acanthium are synonyms defined as:

cotton thistle and Onopordum acanthium: biennial Eurasian white hairy thistle having pale purple flowers; naturalized in North America

Other synonyms of cotton thistle include Onopordon acanthium, Scotch thistle, woolly thistle.

cotton thistle (noun)	Onopordum acanthium (noun)
biennial Eurasian white hairy thistle having pale purple flowers; naturalized in North America	biennial Eurasian white hairy thistle having pale purple flowers; naturalized in North America