The Collaborative International Dictionary of English v.0.48:

Sole \Sole\, n. [F. sole, L. solea; -- so named from its flat
   shape. See Sole of the foot.] (Zool.)
   (a) Any one of several species of flatfishes of the genus
       Solea and allied genera of the family Soleidae,
       especially the common European species (Solea
       vulgaris), which is a valuable food fish.
   (b) Any one of several American flounders somewhat resembling
       the true sole in form or quality, as the California sole
       (Lepidopsetta bilineata), the long-finned sole
       (Glyptocephalus zachirus), and other species.
       [1913 Webster]

   Lemon, or French, sole (Zool.), a European species of
      sole (Solea pegusa).

   Smooth sole (Zool.), the megrim.
      [1913 Webster]