sea robber

from WordNet (r) 3.0 (2006)

sea robber
    n 1: 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}, {sea rover}]

from The Collaborative International Dictionary of English v.0.48

Sea robber \Sea" rob"ber\
   A pirate; a sea rover.
   [1913 Webster]