The Collaborative International Dictionary of English v.0.48:

Radula \Rad"u*la\ (r[a^]d"[-u]*l[.a]), n.; pl. Radulae
   (r[a^]d"[-u]*l[=e]). [L., a scraper, fr. radere to scrape.]
   (Zool.)
   The chitinous ribbon bearing the teeth of mollusks; -- called
   also lingual ribbon, and tongue. See Odontophore.
   [1913 Webster]