The Collaborative International Dictionary of English v.0.48:

Charlock \Char"lock\, n. [AS. cerlic; the latter part perh. fr.
   AS. le['a]c leek. Cf. Hemlock.] (Bot.)
   A cruciferous plant (Brassica sinapistrum) with yellow
   flowers; wild mustard. It is troublesome in grain fields.
   Called also chardock, chardlock, chedlock, and
   kedlock.
   [1913 Webster]

   Jointed charlock, White charlock, a troublesome weed
      (Raphanus Raphanistrum) with straw-colored, whitish, or
      purplish flowers, and jointed pods: wild radish.
      [1913 Webster]

WordNet (r) 3.0 (2006):

jointed charlock
    n 1: Eurasian weed having yellow or mauve or white flowers and
         podlike fruits [syn: jointed charlock, wild radish,
         wild rape, runch, Raphanus raphanistrum]