Ulmus thomasii vs rock elm

Ulmus thomasii and rock elm both are nouns.

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

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

Ulmus thomasii and rock elm: tall widely distributed elm of eastern North America

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