leatherneck vs devil dog

leatherneck and devil dog both are nouns.

Word	Noun	Adjective	Verb	Adverb
leatherneck	Yes	No	No	No
devil dog	Yes	No	No	No

As nouns, leatherneck and devil dog are synonyms defined as:

Other synonyms of leatherneck include Marine, shipboard soldier.

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