DuckCorp Dico

Found one definition

1.                 From The Collaborative International Dictionary of English v.0.48:
                   
   
   
                   
                     
   Sao \Sa"o\, n. (Zool.)
      Any marine annelid of the genus Hyalinaecia, especially
      Hyalinaecia tubicola of Europe, which inhabits a
      transparent movable tube resembling a quill in color and
      texture.
      [1913 Webster]