Source : Webster's Revised Unabridged Dictionary (1913)

Horntail \Horn"tail`\, n. (Zo["o]l.)
   Any one of family ({Urocerid[ae]}) of large hymenopterous
   insects, allied to the sawflies. The larv[ae] bore in the
   wood of trees. So called from the long, stout ovipositors of
   the females.