Wordnet 3.0
NOUN (1)
1. 
 any of various marine gastropods of the suborder Nudibranchia having a shell-less and often beautifully colored body; 
[syn: sea slug, nudibranch]
The Collaborative International Dictionary of English v.0.48:
Nudibranch \Nu"di*branch\, a. (Zool.)
   Of or pertaining to the Nudibranchiata. -- n. One of the
   Nudibranchiata.
   [1913 Webster]
WordNet (r) 3.0 (2006):
nudibranch
    n 1: any of various marine gastropods of the suborder
         Nudibranchia having a shell-less and often beautifully
         colored body [syn: sea slug, nudibranch]