Wordnet 3.0
NOUN (1)
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]
The Collaborative International Dictionary of English v.0.48:
Sea robber \Sea" rob"ber\
   A pirate; a sea rover.
   [1913 Webster]
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]