hellebore vs bugbane

hellebore and bugbane both are nouns.

Word	Noun	Adjective	Verb	Adverb
hellebore	Yes	No	No	No
bugbane	Yes	No	No	No

As nouns, bugbane is a hyponym of hellebore; that is, bugbane is a word with a more specific, narrower meaning than hellebore:

hellebore: perennial herbs of the lily family having thick toxic rhizomes
bugbane: North American plant having large leaves and yellowish green flowers growing in racemes; yields a toxic alkaloid used medicinally

Other hyponyms of hellebore include American hellebore, Indian poke, Veratrum viride, white hellebore.

hellebore (noun)	bugbane (noun)
any plant of the Eurasian genus Helleborus	a plant of the genus Cimicifuga having flowers in long racemes or panicles reported to be distasteful to insects
perennial herbs of the lily family having thick toxic rhizomes	North American plant having large leaves and yellowish green flowers growing in racemes; yields a toxic alkaloid used medicinally