boater vs rower

boater and rower both are nouns.

Word	Noun	Adjective	Verb	Adverb
boater	Yes	No	No	No
rower	Yes	No	No	No

As nouns, rower is a hyponym of boater; that is, rower is a word with a more specific, narrower meaning than boater:

Other hyponyms of boater include canoeist, paddler, ferryman, gondolier, gondoliere, punter.

boater (noun)	rower (noun)
a stiff hat made of straw with a flat crown	someone who rows a boat
someone who drives or rides in a boat