Source : Webster's Revised Unabridged Dictionary (1913)

Hornbug \Horn"bug`\, n. (Zo["o]l.)
   A large nocturnal beetle of the genus {Lucanus} (as {L.
   capreolus}, and {L. dama}), having long, curved upper jaws,
   resembling a sickle. The grubs are found in the trunks of old
   trees.