river boat vs boat

river boat and boat both are nouns.

Word	Noun	Adjective	Verb	Adverb
river boat	Yes	No	No	No
boat	Yes	No	Yes	No

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

river boat (noun)	boat (noun)
a boat used on rivers or to ply a river	a small vessel for travel on water
	a dish (often boat-shaped) for serving gravy or sauce

river boat (verb)	boat (verb)
	ride in a boat on water