river gum vs eucalypt

river gum and eucalypt both are nouns.

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

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

river gum: somewhat crooked red gum tree growing chiefly along rivers; has durable reddish lumber used in heavy construction
eucalypt: a tree of the genus Eucalyptus

Other hypernyms of river gum include eucalyptus, eucalyptus tree.

river gum (noun)	eucalypt (noun)
somewhat crooked red gum tree growing chiefly along rivers; has durable reddish lumber used in heavy construction	a tree of the genus Eucalyptus