pillager vs sea rover

pillager and sea rover both are nouns.

Word	Noun	Adjective	Verb	Adverb
pillager	Yes	No	No	No
sea rover	Yes	No	No	No

As nouns, sea rover is a hyponym of pillager; that is, sea rover is a word with a more specific, narrower meaning than pillager:

pillager: someone who takes spoils or plunder (as in war)
sea rover: someone who robs at sea or plunders the land from the sea without having a commission from any sovereign nation

Other hyponyms of pillager include buccaneer, pirate, sea robber.

pillager (noun)	sea rover (noun)
someone who takes spoils or plunder (as in war)	someone who robs at sea or plunders the land from the sea without having a commission from any sovereign nation