The Collaborative International Dictionary of English v.0.48:

Elytron \El"y*tron\ (?; 277), Elytrum \El"y*trum\ (-tr?m)n.; pl.
   Elytra. [NL., fr. Gr. ?, fr. ? to roll round.] (Zo["o]l.)
   (a) One of the anterior pair of wings in the Coleoptera and
       some other insects, when they are thick and serve only as
       a protection for the posterior pair. See Coleoptera.
   (b) One of the shieldlike dorsal scales of certain annelids.
       See Ch[ae]topoda.
       [1913 Webster]

WordNet (r) 3.0 (2006):

elytron
    n 1: either of the horny front wings in beetles and some other
         insects which cover and protect the functional hind wings
         [syn: wing case, elytron]