cotton thistle vs Scotch thistle

cotton thistle and Scotch thistle both are nouns.

Word	Noun	Adjective	Verb	Adverb
cotton thistle	Yes	No	No	No
Scotch thistle	Yes	No	No	No

As nouns, cotton thistle and Scotch thistle are synonyms defined as:

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

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

cotton thistle (noun)	Scotch thistle (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