sea robber vs corsair

sea robber and corsair both are nouns.

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

As nouns, corsair is a hyponym of sea robber; that is, corsair is a word with a more specific, narrower 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
corsair: a pirate along the Barbary Coast

Other hyponyms of sea robber include Barbary pirate, sea king.

sea robber (noun)	corsair (noun)
someone who robs at sea or plunders the land from the sea without having a commission from any sovereign nation	a swift pirate ship (often operating with official sanction)
	a pirate along the Barbary Coast