river gum vs eucalyptus

river gum and eucalyptus both are nouns.

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

As nouns, eucalyptus is a hypernym of river gum; that is, eucalyptus 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
eucalyptus: a tree of the genus Eucalyptus

Other hypernyms of river gum include eucalypt, eucalyptus tree.

river gum (noun)	eucalyptus (noun)
somewhat crooked red gum tree growing chiefly along rivers; has durable reddish lumber used in heavy construction	a tree of the genus Eucalyptus
	wood of any of various eucalyptus trees valued as timber