mountain ash vs eucalypt

mountain ash and eucalypt both are nouns.

Word	Noun	Adjective	Verb	Adverb
mountain ash	Yes	No	No	No
eucalypt	Yes	No	No	No

As nouns, eucalypt is a hypernym of mountain ash; that is, eucalypt is a word with a broader meaning than mountain ash:

mountain ash: tree having wood similar to the alpine ash; tallest tree in Australia and tallest hardwood in the world
eucalypt: a tree of the genus Eucalyptus

Other hypernyms of mountain ash include eucalyptus, eucalyptus tree.

mountain ash (noun)	eucalypt (noun)
any of various trees of the genus Sorbus	a tree of the genus Eucalyptus
low-growing ash of Texas
tree having wood similar to the alpine ash; tallest tree in Australia and tallest hardwood in the world