azalea vs rhododendron

azalea and rhododendron both are nouns.

Word	Noun	Adjective	Verb	Adverb
azalea	Yes	No	No	No
rhododendron	Yes	No	No	No

As nouns, rhododendron is a hypernym of azalea; that is, rhododendron is a word with a broader meaning than azalea:

azalea: any of numerous ornamental shrubs grown for their showy flowers of various colors
rhododendron: any shrub of the genus Rhododendron: evergreen shrubs or small shrubby trees having leathery leaves and showy clusters of campanulate (bell-shaped) flowers

azalea (noun)	rhododendron (noun)
any of numerous ornamental shrubs grown for their showy flowers of various colors	any shrub of the genus Rhododendron: evergreen shrubs or small shrubby trees having leathery leaves and showy clusters of campanulate (bell-shaped) flowers