The Collaborative International Dictionary of English v.0.48:

daikon \daikon\ n.
   a radish of Japan (Raphanus sativus longipinnatus) with a
   long hard durable root eaten raw or cooked.

   Syn: Japanese radish, Raphanus sativus longipinnatus.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Raphanus sativus longipinnatus
    n 1: radish of Japan with a long hard durable root eaten raw or
         cooked [syn: radish, daikon, Japanese radish,
         Raphanus sativus longipinnatus]