ghost gum vs eucalypt

ghost gum and eucalypt both are nouns.

Word	Noun	Adjective	Verb	Adverb
ghost gum	Yes	No	No	No
eucalypt	Yes	No	No	No

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

ghost gum: small to medium-sized tree of Australia and Tasmania having smooth white to light-grey bark shedding in patches or strips
eucalypt: a tree of the genus Eucalyptus

Other hypernyms of ghost gum include eucalyptus, eucalyptus tree.

ghost gum (noun)	eucalypt (noun)
small to medium-sized tree of Australia and Tasmania having smooth white to light-grey bark shedding in patches or strips	a tree of the genus Eucalyptus