white cedar vs American arborvitae

white cedar and American arborvitae both are nouns.

Word	Noun	Adjective	Verb	Adverb
white cedar	Yes	No	No	No
American arborvitae	Yes	No	No	No

As nouns, white cedar and American arborvitae are synonyms defined as:

white cedar and American arborvitae: small evergreen of eastern North America having tiny scalelike leaves on flattened branchlets

Other synonyms of white cedar include northern white cedar, Thuja occidentalis.

white cedar (noun)	American arborvitae (noun)
slow-growing medium-sized cedar of east coast of the United States; resembles American arborvitae	small evergreen of eastern North America having tiny scalelike leaves on flattened branchlets
small evergreen of eastern North America having tiny scalelike leaves on flattened branchlets