Source : Webster's Revised Unabridged Dictionary (1913)

Sea cucumber \Sea" cu"cum*ber\ (Zo["o]l.)
   Any large holothurian, especially one of those belonging to
   the genus {Pentacta}, or {Cucumaria}, as the common American
   and European species. ({P. frondosa}).

Source : WordNet®

sea cucumber
     n : echinoderm having a flexible sausage-shaped body, tentacles
         surrounding the mouth and tube feet; free-living mud
         feeders: sea cucumbers [syn: {holothurian}]