slippery elm vs elm tree

slippery elm and elm tree both are nouns.

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

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

slippery elm: North American elm having rough leaves that are red when opening; yields a hard wood
elm tree: any of various trees of the genus Ulmus: important timber or shade trees

Other hypernyms of slippery elm include elm.

slippery elm (noun)	elm tree (noun)
North American elm having rough leaves that are red when opening; yields a hard wood	any of various trees of the genus Ulmus: important timber or shade trees