1. a large (25 mm, or 0.98 in, or greater) insect in the family Siricidae and with both sexes having a hornlike process at the end of the abdomen —note horntails have thick waists; wasps (Vespidae), bees (Apidae), and ants (Formicidae) have narrow waists —synonym woodwasp 2. a short spine on the last body segment of Siricid larvae, for which they are namedThis definition last updated 10/28/2008