The Collaborative International Dictionary of English v.0.48:

Radish \Rad"ish\ (r[a^]d"[i^]sh), n. [F. radis; cf. It. radice,
   Pr. raditz: all fr. L. radix, -icis, a root, an edible root,
   especially a radish, akin to E. wort. See Wort, and cf.
   Eradicate, Race a root, Radix.] (Bot.)
   The pungent fleshy root of a well-known cruciferous plant
   (Raphanus sativus); also, the whole plant.
   [1913 Webster]

   Radish fly (Zool.), a small two-winged fly (Anthomyia
      raphani) whose larvae burrow in radishes. It resembles
      the onion fly.

   Rat-tailed radish (Bot.), an herb (Raphanus caudatus)
      having a long, slender pod, which is sometimes eaten.

   Wild radish (Bot.), the jointed charlock.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Raphanus sativus
    n 1: Eurasian plant widely cultivated for its edible pungent
         root usually eaten raw [syn: radish, Raphanus sativus]