raider vs sea rover

raider and sea rover both are nouns.

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

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

raider: 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 raider include buccaneer, pirate, sea robber.

raider (noun)	sea rover (noun)
a corporate investor who intends to take over a company by buying a controlling interest in its stock and installing new management	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)