witch elm vs elm tree

witch elm and elm tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
witch elm	Yes	No	No	No
elm tree	Yes	No	No	No

As nouns, elm tree is a hypernym of witch elm; that is, elm tree is a word with a broader meaning than witch elm:

witch elm: Eurasian elm often planted as a shade tree
elm tree: any of various trees of the genus Ulmus: important timber or shade trees

Other hypernyms of witch elm include elm.

witch elm (noun)	elm tree (noun)
Eurasian elm often planted as a shade tree	any of various trees of the genus Ulmus: important timber or shade trees