sailor vs water rat

sailor and water rat both are nouns.

Word	Noun	Adjective	Verb	Adverb
sailor	Yes	No	No	No
water rat	Yes	No	No	No

As nouns, water rat is a hyponym of sailor; that is, water rat is a word with a more specific, narrower meaning than sailor:

Other hyponyms of sailor include hand, lascar, gob, Jack-tar, Jack, mariner, old salt, sea dog, seafarer, seaman, tar, water dog, yachtsperson.

sailor (noun)	water rat (noun)
a stiff hat made of straw with a flat crown	any of various amphibious rats
any member of a ship's crew	common large Eurasian vole
a serviceman in the navy	a person who enjoys being in or on the water