sea robber vs despoiler

sea robber and despoiler both are nouns.

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

As nouns, despoiler is a hypernym of sea robber; that is, despoiler is a word with a broader meaning than sea robber:

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

Other hypernyms of sea robber include freebooter, looter, pillager, plunderer, raider, spoiler.

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