Source : Webster's Revised Unabridged Dictionary (1913)

Sea rover \Sea" rov"er\
   One that cruises or roves the sea for plunder; a sea robber;
   a pirate; also, a piratical vessel.

Source : WordNet®

sea rover
     n : someone who robs at sea or plunders the land from the sea
         without having a commission from any sovereign nation
         [syn: {pirate}, {buccaneer}, {sea robber}]