The Collaborative International Dictionary of English v.0.48:

Cicada \Ci*ca"da\ (s[i^]*k[=a]"d[.a]), n.; pl. E. Cicadas
   (-d[.a]z), L. Cicad[ae] (-d[=e]). [L.] (Zool.)
   Any species of the genus Cicada or of the family
   Cicadidae. They are large hemipterous insects, with nearly
   transparent wings. The male makes a shrill sound by peculiar
   organs in the under side of the abdomen, consisting of a pair
   of stretched membranes, acted upon by powerful muscles. A
   noted American species (Cicada septendecim) is called the
   seventeen year locust. Another common species is the
   dogday cicada.

   Syn: cicala. [1913 Webster]

WordNet (r) 3.0 (2006):

cicada
    n 1: stout-bodied insect with large membranous wings; male has
         drum-like organs for producing a high-pitched drone [syn:
         cicada, cicala]