shipboard soldier vs leatherneck

shipboard soldier and leatherneck both are nouns.

Word	Noun	Adjective	Verb	Adverb
shipboard soldier	Yes	No	No	No
leatherneck	Yes	No	No	No

As nouns, shipboard soldier and leatherneck are synonyms defined as:

shipboard soldier and leatherneck: a member of the United States Marine Corps

Other synonyms of shipboard soldier include devil dog, Marine.

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