viper's bugloss vs blue thistle

viper's bugloss and blue thistle both are nouns.

Word	Noun	Adjective	Verb	Adverb
viper's bugloss	Yes	No	No	No
blue thistle	Yes	No	No	No

As nouns, viper's bugloss and blue thistle are synonyms defined as:

viper's bugloss and blue thistle: a coarse prickly European weed with spikes of blue flowers; naturalized in United States

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

viper's bugloss (noun)	blue thistle (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