DuckCorp Dico

Found one definition

1.                 From The Collaborative International Dictionary of English v.0.48:
                   
   
   
                   
                     
   SOS \SOS\
      The letters signified by the signal ( . . . --- . . . )
      prescribed by the International Radiotelegraphic Convention
      of 1912 for use by ships in distress.
      [Webster 1913 Suppl.]