sailor vs water dog

sailor and water dog both are nouns.

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

As nouns, water dog is a hyponym of sailor; that is, water dog 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 rat, yachtsperson.

sailor (noun)	water dog (noun)
a stiff hat made of straw with a flat crown	a dog accustomed to water and usually trained to retrieve waterfowl
any member of a ship's crew	a person who enjoys being in or on the water
a serviceman in the navy