Search Result for "ommatidium": 
Wordnet 3.0

NOUN (1)

1. any of the numerous small cone-shaped eyes that make up the compound eyes of some arthropods; 



The Collaborative International Dictionary of English v.0.48:

Ommatidium \Om`ma*tid"i*um\, n.; pl. Ommatidia. [NL., dim. of
   Gr. ?, ?, the eye.] (Zool.)
   One of the single eyes forming the compound eyes of
   crustaceans, insects, and other invertebrates; one of the
   eyes of an ommateum.
   [1913 Webster]


WordNet (r) 3.0 (2006):

ommatidium
    n 1: any of the numerous small cone-shaped eyes that make up the
         compound eyes of some arthropods