stinking horehound vs black horehound

stinking horehound and black horehound both are nouns.

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

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

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

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

stinking horehound (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