The Collaborative International Dictionary of English v.0.48:

Peppergrass \Pep"per*grass`\, n. (Bot.)
   (a) Any herb of the cruciferous genus Lepidium, especially
       the garden peppergrass, or garden cress, Lepidium
       sativum; -- called also pepperwort. All the species
       have a pungent flavor.
   (b) The common pillwort of Europe (Pilularia globulifera).
       See Pillwort.
       [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

   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.
         [1913 Webster]

               To strip the brook with mantling cresses spread.
                                                  --Goldsmith.
         [1913 Webster]

   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.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Lepidium sativum
    n 1: annual herb used as salad green and garnish [syn: common
         garden cress, garden pepper cress, pepper grass,
         pepperwort, Lepidium sativum]