Source : Webster's Revised Unabridged Dictionary (1913)

Viking \Vi"king\, n. [Icel. v[=i]kingr, fr. v[=i]k a bay,
   inlet.]
   One belonging to the pirate crews from among the Northmen,
   who plundered the coasts of Europe in the eighth, ninth, and
   tenth centuries.

         Of grim Vikings, and the rapture Of the sea fight, and
         the capture, And the life of slavery.    --Longfellow.

   Note: Vikings differs in meaning from sea king, with which
         frequently confounded. ``The sea king was a man
         connected with a royal race, either of the small kings
         of the country, or of the Haarfager family, and who, by
         right, received the title of king as soon he took the
         command of men, although only of a single ship's crew,
         and without having any land or kingdom . . . Vikings
         were merely pirates, alternately peasants and pirates,
         deriving the name of viking from the vicks, wicks, or
         inlets, on the coast in which they harbored with their
         long ships or rowing galleys.'' --Laing.

Source : WordNet®

Viking
     n : any of the Scandinavian people who raided the coasts of
         Europe from the 8th to the 11th centuries