boater vs ferryman

boater and ferryman both are nouns.

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

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

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

boater (noun)	ferryman (noun)
a stiff hat made of straw with a flat crown	a man who operates a ferry
someone who drives or rides in a boat