cup and saucer vs bellflower

cup and saucer and bellflower both are nouns.

Word	Noun	Adjective	Verb	Adverb
cup and saucer	Yes	No	No	No
bellflower	Yes	No	No	No

As nouns, bellflower is a hypernym of cup and saucer; that is, bellflower is a word with a broader meaning than cup and saucer:

cup and saucer: European biennial widely cultivated for its blue or violet or white flowers
bellflower: any of various plants of the genus Campanula having blue or white bell-shaped flowers

Other hypernyms of cup and saucer include campanula.

cup and saucer (noun)	bellflower (noun)
European biennial widely cultivated for its blue or violet or white flowers	any of various plants of the genus Campanula having blue or white bell-shaped flowers