blue thistle vs blueweed

blue thistle and blueweed both are nouns.

Word	Noun	Adjective	Verb	Adverb
blue thistle	Yes	No	No	No
blueweed	Yes	No	No	No

As nouns, blue thistle and blueweed are synonyms defined as:

blue thistle and blueweed: a coarse prickly European weed with spikes of blue flowers; naturalized in United States

Other synonyms of blue thistle include blue devil, Echium vulgare, viper's bugloss.

blue thistle (noun)	blueweed (noun)
a coarse prickly European weed with spikes of blue flowers; naturalized in United States	a coarse prickly European weed with spikes of blue flowers; naturalized in United States