sweet William vs garden pink

sweet William and garden pink both are nouns.

Word	Noun	Adjective	Verb	Adverb
sweet William	Yes	No	No	No
garden pink	Yes	No	No	No

As nouns, garden pink is a hypernym of sweet William; that is, garden pink is a word with a broader meaning than sweet William:

sweet William: Eurasian pink widely cultivated for its flat-topped dense clusters of varicolored flowers
garden pink: any of various flowers of plants of the genus Dianthus cultivated for their fragrant flowers

Other hypernyms of sweet William include pink.

sweet William (noun)	garden pink (noun)
Eurasian pink widely cultivated for its flat-topped dense clusters of varicolored flowers	any of various flowers of plants of the genus Dianthus cultivated for their fragrant flowers