Eucalyptus regnans vs eucalypt

Eucalyptus regnans and eucalypt both are nouns.

Word	Noun	Adjective	Verb	Adverb
Eucalyptus regnans	Yes	No	No	No
eucalypt	Yes	No	No	No

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

Eucalyptus regnans: 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 Eucalyptus regnans include eucalyptus, eucalyptus tree.

Eucalyptus regnans (noun)	eucalypt (noun)
tree having wood similar to the alpine ash; tallest tree in Australia and tallest hardwood in the world	a tree of the genus Eucalyptus