Marine vs military man

Marine and military man both are nouns.

Word	Noun	Adjective	Verb	Adverb
Marine	Yes	No	No	No
military man	Yes	No	No	No

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

Marine: a member of the United States Marine Corps
military man: someone who serves in the armed forces; a member of a military force

Other hypernyms of Marine include man, military personnel, serviceman.

Marine (noun)	military man (noun)
a member of the United States Marine Corps	someone who serves in the armed forces; a member of a military force