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]