Ulmus americana vs rock elm

Ulmus americana and rock elm both are nouns.

Word	Noun	Adjective	Verb	Adverb
Ulmus americana	Yes	No	No	No
rock elm	Yes	No	No	No

As nouns, Ulmus americana and rock elm are synonyms defined as:

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

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

Ulmus americana (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