Source : Webster's Revised Unabridged Dictionary (1913)

Water cress \Wa"ter cress`\ (Bot.)
   A perennial cruciferous herb ({Nasturtium officinale})
   growing usually in clear running or spring water. The leaves
   are pungent, and used for salad and as an antiscorbutic.

Cress \Cress\ (kr[e^]s), n.; pl. {Cresses} (kr[e^]s"[e^]z). [OE.
   ces, cresse, kers, kerse, AS. cresse, cerse; akin to D. kers,
   G. kresse, Dan. karse, Sw. krasse, and possibly also to OHG.
   chresan to creep.] (Bot.)
   A plant of various species, chiefly cruciferous. The leaves
   have a moderately pungent taste, and are used as a salad and
   antiscorbutic.

   Note: The garden cress, called also {peppergrass}, is the
         {Lepidium sativum}; the water cress is the {Nasturtium
         officinale}. Various other plants are sometimes called
         cresses.

               To strip the brook with mantling cresses spread.
                                                  --Goldsmith.

   {Bitter cress}. See under {Bitter}.

   {Not worth a cress}, or {``not worth a kers.''} a common old
      proverb, now turned into the meaningless ``not worth a
      curse.'' --Skeat.

Source : WordNet®

Nasturtium officinale
     n : perennial Eurasian cress growing chiefly in springs or
         running water having fleshy pungent leaves used in salads
         or as a potherb or garnish; introduced in North America
         and elsewhere [syn: {common watercress}, {Rorippa
         nasturtium-aquaticum}]