serviceman vs sailor

serviceman and sailor both are nouns.

Word	Noun	Adjective	Verb	Adverb
serviceman	Yes	No	No	No
sailor	Yes	No	No	No

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

serviceman: someone who serves in the armed forces; a member of a military force
sailor: a serviceman in the navy

serviceman (noun)	sailor (noun)
someone who serves in the armed forces; a member of a military force	a stiff hat made of straw with a flat crown
	any member of a ship's crew
	a serviceman in the navy