sea king vs sea rover

sea king and sea rover both are nouns.

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

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

sea king: a Viking pirate chief
sea rover: someone who robs at sea or plunders the land from the sea without having a commission from any sovereign nation

Other hypernyms of sea king include buccaneer, pirate, sea robber.

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