river boat vs keelboat

river boat and keelboat both are nouns.

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

As nouns, keelboat is a hyponym of river boat; that is, keelboat is a word with a more specific, narrower meaning than river boat:

river boat: a boat used on rivers or to ply a river
keelboat: river boat with a shallow draught and a keel but no sails; used to carry freight; moved by rowing or punting or towing

Other hyponyms of river boat include showboat.

river boat (noun)	keelboat (noun)
a boat used on rivers or to ply a river	river boat with a shallow draught and a keel but no sails; used to carry freight; moved by rowing or punting or towing