ranger vs serviceman

ranger and serviceman both are nouns.

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

As nouns, serviceman is a hypernym of ranger; that is, serviceman is a word with a broader meaning than ranger:

ranger: a member of a military unit trained as shock troops for hit-and-run raids
serviceman: someone who serves in the armed forces; a member of a military force

Other hypernyms of ranger include man, military man, military personnel.

ranger (noun)	serviceman (noun)
an official who is responsible for managing and protecting an area of forest	someone who serves in the armed forces; a member of a military force
a member of a military unit trained as shock troops for hit-and-run raids