The Collaborative International Dictionary of English v.0.48:

Cole \Cole\ (k[=o]l), n. [OE. col, caul, AS. cawl, cawel, fr. L.
   caulis, the stalk or stem of a plant, esp. a cabbage stalk,
   cabbage, akin to Gr. kaylo`s. Cf. Cauliflower, Kale.]
   (Bot.)
   A plant of the Brassica or Cabbage genus; esp. that form of
   Brassica oleracea called rape and coleseed.
   [1913 Webster]

WordNet (r) 3.0 (2006):

cole
    n 1: a hardy cabbage with coarse curly leaves that do not form a
         head [syn: kale, kail, cole, borecole, colewort,
         Brassica oleracea acephala]
    2: coarse curly-leafed cabbage [syn: kale, kail, cole]