The Collaborative International Dictionary of English v.0.48:

Diptera \Dip"te*ra\, n. pl. [NL., fr. Gr. ? with two wings, di-
   = di`s- twice + ? feather, wing: cf. F. dipt[`e]re.] (Zool.)
   An extensive order of insects having only two functional
   wings and two balancers, as the house fly, mosquito, etc.
   They have a suctorial proboscis, often including two pairs of
   sharp organs (mandibles and maxill[ae]) with which they
   pierce the skin of animals. They undergo a complete
   metamorphosis, their larv[ae] (called maggots) being usually
   without feet.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Diptera
    n 1: a large order of insects having a single pair of wings and
         sucking or piercing mouths; includes true flies and
         mosquitoes and gnats and crane flies [syn: Diptera,
         order Diptera]