The Collaborative International Dictionary of English v.0.48:

Mariner \Mar"i*ner\, n. [F. marinier, LL. marinarius. See
   Marine.]
   One whose occupation is to assist in navigating ships; a
   seaman or sailor. --Chaucer.
   [1913 Webster]

   Mariner's compass. See under Compass.
      [1913 Webster]

WordNet (r) 3.0 (2006):

mariner
    n 1: a man who serves as a sailor [syn: mariner, seaman,
         tar, Jack-tar, Jack, old salt, seafarer, gob,
         sea dog]