hoya vs honey plant

hoya and honey plant both are nouns.

Word	Noun	Adjective	Verb	Adverb
hoya	Yes	No	No	No
honey plant	Yes	No	No	No

As nouns, honey plant is a hyponym of hoya; that is, honey plant is a word with a more specific, narrower meaning than hoya:

hoya: any plant of the genus Hoya having fleshy leaves and usually nectariferous flowers
honey plant: a plant that furnishes nectar suitable for making honey

Other hyponyms of hoya include Hoya carnosa, wax plant.

hoya (noun)	honey plant (noun)
any plant of the genus Hoya having fleshy leaves and usually nectariferous flowers	a plant that furnishes nectar suitable for making honey