leatherneck vs military man

leatherneck and military man both are nouns.

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

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

leatherneck: 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 leatherneck include man, military personnel, serviceman.

leatherneck (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