military officer vs serviceman

military officer and serviceman both are nouns.

Word	Noun	Adjective	Verb	Adverb
military officer	Yes	No	No	No
serviceman	Yes	No	No	No

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

military officer: any person in the armed services who holds a position of authority or command
serviceman: someone who serves in the armed forces; a member of a military force

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

military officer (noun)	serviceman (noun)
any person in the armed services who holds a position of authority or command	someone who serves in the armed forces; a member of a military force