sea robber vs sea king

sea robber and sea king both are nouns.

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

As nouns, sea king is a hyponym of sea robber; that is, sea king 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
sea king: a Viking pirate chief

Other hyponyms of sea robber include Barbary pirate, corsair.

sea robber (noun)	sea king (noun)
someone who robs at sea or plunders the land from the sea without having a commission from any sovereign nation	a Viking pirate chief