shipboard soldier vs Marine

shipboard soldier and Marine both are nouns.

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

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

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

Other synonyms of shipboard soldier include devil dog, leatherneck.

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