hippo vs river horse

hippo and river horse both are nouns.

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

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

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

Other synonyms of hippo include hippopotamus, Hippopotamus amphibius.

hippo (noun)	river horse (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