European elm vs elm tree

European elm and elm tree both are nouns.

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

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

European elm: broad spreading rough-leaved elm common throughout Europe and planted elsewhere
elm tree: any of various trees of the genus Ulmus: important timber or shade trees

Other hypernyms of European elm include elm.

European elm (noun)	elm tree (noun)
broad spreading rough-leaved elm common throughout Europe and planted elsewhere	any of various trees of the genus Ulmus: important timber or shade trees