The Collaborative International Dictionary of English v.0.48:

Prognathism \Prog"na*thism\ (pr[o^]g"n[.a]*th[i^]z'm or
   pr[o^]g*n[=a]"th[i^]z'm), n. (Anat.)
   Projection of the jaws. -- Prog"na*thy, n.
   [1913 Webster]