The Collaborative International Dictionary of English v.0.48:

Hornet \Hor"net\, n. [AS. hyrnet; akin to OHG. hornaz, hornuz,
   G. horniss; perh. akin to E. horn, and named from the sound
   it makes as if blowing the horn; but more prob. akin to D.
   horzel, Lith. szirszone, L. crabo.] (Zool.)
   A large, strong wasp. The European species (Vespa crabro)
   is of a dark brown and yellow color. It is very pugnacious,
   and its sting is very severe. Its nest is constructed of a
   paperlike material, and the layers of comb are hung together
   by columns. The American white-faced hornet (Vespa
   maculata) is larger and has similar habits.
   [1913 Webster]

   Hornet fly (Zool.), any dipterous insect of the genus
      Asilus, and allied genera, of which there are numerous
      species. They are large and fierce flies which capture
      bees and other insects, often larger than themselves, and
      suck their blood. Called also hawk fly, robber fly.

   To stir up a hornet's nest, to provoke the attack of a
      swarm of spiteful enemies or spirited critics. [Colloq.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

hornet
    n 1: large stinging paper wasp

Easton's 1897 Bible Dictionary:

Hornet
   Heb. tsir'ah, "stinging", (Ex. 23:28; Deut. 7:20; Josh. 24:12).
   The word is used in these passages as referring to some means by
   which the Canaanites were to be driven out from before the
   Israelites. Some have supposed that the word is used in a
   metaphorical sense as the symbol of some panic which would seize
   the people as a "terror of God" (Gen. 35:5), the consternation
   with which God would inspire the Canaanites. In Palestine there
   are four species of hornets, differing from our hornets, being
   larger in size, and they are very abundant. They "attack human
   beings in a very furious manner." "The furious attack of a swarm
   of hornets drives cattle and horses to madness, and has even
   caused the death of the animals."