black archangel vs black horehound

black archangel and black horehound both are nouns.

Word	Noun	Adjective	Verb	Adverb
black archangel	Yes	No	No	No
black horehound	Yes	No	No	No

As nouns, black archangel and black horehound are synonyms defined as:

black archangel and black horehound: ill-smelling European herb with rugose leaves and whorls of dark purple flowers

Other synonyms of black archangel include Ballota nigra, fetid horehound, stinking horehound.

black archangel (noun)	black horehound (noun)
ill-smelling European herb with rugose leaves and whorls of dark purple flowers	ill-smelling European herb with rugose leaves and whorls of dark purple flowers