poisonous nightshade vs bittersweet nightshade

poisonous nightshade and bittersweet nightshade both are nouns.

Word	Noun	Adjective	Verb	Adverb
poisonous nightshade	Yes	No	No	No
bittersweet nightshade	Yes	No	No	No

As nouns, poisonous nightshade and bittersweet nightshade are synonyms defined as:

poisonous nightshade and bittersweet nightshade: poisonous perennial Old World vine having violet flowers and oval coral-red berries; widespread weed in North America

Other synonyms of poisonous nightshade include bittersweet, climbing nightshade, deadly nightshade, Solanum dulcamara, woody nightshade.

poisonous nightshade (noun)	bittersweet nightshade (noun)
poisonous perennial Old World vine having violet flowers and oval coral-red berries; widespread weed in North America	poisonous perennial Old World vine having violet flowers and oval coral-red berries; widespread weed in North America