river horse vs hippo

river horse and hippo both are nouns.

Word	Noun	Adjective	Verb	Adverb
river horse	Yes	No	No	No
hippo	Yes	No	No	No

As nouns, river horse and hippo are synonyms defined as:

river horse and hippo: massive thick-skinned herbivorous animal living in or around rivers of tropical Africa

Other synonyms of river horse include hippopotamus, Hippopotamus amphibius.

river horse (noun)	hippo (noun)
massive thick-skinned herbivorous animal living in or around rivers of tropical Africa	massive thick-skinned herbivorous animal living in or around rivers of tropical Africa