The Collaborative International Dictionary of English v.0.48:

Runch \Runch\, n. (Bot.)
   The wild radish. --Dr. Prior.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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