waterman vs rower

waterman and rower both are nouns.

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

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

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

waterman (noun)	rower (noun)
someone who drives or rides in a boat	someone who rows a boat