The Collaborative International Dictionary of English v.0.48:

Artichoke \Ar"ti*choke\, n. [It. articiocco, perh. corrupted fr.
   the same word as carciofo; cf. older spellings archiciocco,
   archicioffo, carciocco, and Sp. alcachofa, Pg. alcachofra;
   prob. fr. Ar. al-harshaf, al-kharsh[=u]f.] (Bot.)
   1. The Cynara scolymus, a plant somewhat resembling a
      thistle, with a dilated, imbricated, and prickly
      involucre. The head (to which the name is also applied) is
      composed of numerous oval scales, inclosing the florets,
      sitting on a broad receptacle, which, with the fleshy base
      of the scales, is much esteemed as an article of food.
      [1913 Webster]

   2. See Jerusalem artichoke.
      [1913 Webster]

WordNet (r) 3.0 (2006):

artichoke
    n 1: Mediterranean thistlelike plant widely cultivated for its
         large edible flower head [syn: artichoke, globe
         artichoke, artichoke plant, Cynara scolymus]
    2: a thistlelike flower head with edible fleshy leaves and heart
       [syn: artichoke, globe artichoke]