sea robber vs raider

sea robber and raider both are nouns.

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

As nouns, raider is a hypernym of sea robber; that is, raider 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
raider: someone who takes spoils or plunder (as in war)

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

sea robber (noun)	raider (noun)
someone who robs at sea or plunders the land from the sea without having a commission from any sovereign nation	a corporate investor who intends to take over a company by buying a controlling interest in its stock and installing new management
	someone who takes spoils or plunder (as in war)