rose campion vs lychnis

rose campion and lychnis both are nouns.

Word	Noun	Adjective	Verb	Adverb
rose campion	Yes	No	No	No
lychnis	Yes	No	No	No

As nouns, lychnis is a hypernym of rose campion; that is, lychnis is a word with a broader meaning than rose campion:

rose campion: an old cottage garden plant of southeastern Europe widely cultivated for its attractive white woolly foliage and showy crimson flowers
lychnis: mostly perennial herbs with sticky stems that catch insects; widespread in north temperate zone

Other hypernyms of rose campion include catchfly.

rose campion (noun)	lychnis (noun)
an old cottage garden plant of southeastern Europe widely cultivated for its attractive white woolly foliage and showy crimson flowers	mostly perennial herbs with sticky stems that catch insects; widespread in north temperate zone