Wordnet 3.0
NOUN (1)
1. 
 fleshy and usually brightly colored cover of some seeds that develops from the ovule stalk and partially or entirely envelopes the seed; 
The Collaborative International Dictionary of English v.0.48:
Aril \Ar"il\, Arillus \A*ril"lus\, n. [From LL. arilli dry
   grapes, perh. fr. L. aridus dry: cf. F,. arille.] (Bot.)
   A exterior covering, forming a false coat or appendage to a
   seed, as the loose, transparent bag inclosing the seed of the
   white water lily. The mace of the nutmeg is also an aril.
   --Gray.
   [1913 Webster] Arllated
   Arillate
WordNet (r) 3.0 (2006):
aril
    n 1: fleshy and usually brightly colored cover of some seeds
         that develops from the ovule stalk and partially or
         entirely envelopes the seed