white elm vs rock elm

white elm and rock elm both are nouns.

Word	Noun	Adjective	Verb	Adverb
white elm	Yes	No	No	No
rock elm	Yes	No	No	No

As nouns, white elm and rock elm are synonyms defined as:

white elm and rock elm: large ornamental tree with graceful gradually spreading branches common in eastern North America

Other synonyms of white elm include American elm, Ulmus americana, water elm.

white elm (noun)	rock elm (noun)
large ornamental tree with graceful gradually spreading branches common in eastern North America	tall widely distributed elm of eastern North America
	large ornamental tree with graceful gradually spreading branches common in eastern North America