Thuja orientalis vs arborvitae

Thuja orientalis and arborvitae both are nouns.

Word	Noun	Adjective	Verb	Adverb
Thuja orientalis	Yes	No	No	No
arborvitae	Yes	No	No	No

As nouns, arborvitae is a hypernym of Thuja orientalis; that is, arborvitae is a word with a broader meaning than Thuja orientalis:

Thuja orientalis: Asiatic shrub or small tree widely planted in United States and Europe; in some classifications assigned to its own genus
arborvitae: any of several Asian and North American conifers of the genera Thuja and Thujopsis

Thuja orientalis (noun)	arborvitae (noun)
Asiatic shrub or small tree widely planted in United States and Europe; in some classifications assigned to its own genus	any of several Asian and North American conifers of the genera Thuja and Thujopsis