'Hornet fly' definitions:

Definition of 'Hornet fly'

From: GCIDE

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]