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.
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.]