pillager vs sea robber

pillager and sea robber both are nouns.

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

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

pillager: someone who takes spoils or plunder (as in war)
sea robber: 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 rover.

pillager (noun)	sea robber (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