Marine vs leatherneck

Marine and leatherneck both are nouns.

Word	Noun	Adjective	Verb	Adverb
Marine	Yes	No	No	No
leatherneck	Yes	No	No	No

As nouns, Marine and leatherneck are synonyms defined as:

Other synonyms of Marine include devil dog, shipboard soldier.

Marine (noun)	leatherneck (noun)
a member of the United States Marine Corps	a member of the United States Marine Corps