What does "cress" mean?

Cress: 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.