boatman vs ferryman

boatman and ferryman both are nouns.

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

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

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

boatman (noun)	ferryman (noun)
someone who drives or rides in a boat	a man who operates a ferry