If a face is prognathous, the jaw sits farther forward than the rest of the face, so the mouth and teeth stick out a little (or a lot) instead of lining up under a flat profile. You almost never hear this in the street. It belongs to science talk: bones, teeth, animal faces, old skulls. A long-snouted dog is an easy picture; a person can be mildly prognathous too, and in those books it is a shape, not a rude remark. Everyday English would just say a sticking-out jaw. Though actually, faces are a mix — one jaw can sit forward while the rest of the head does not — so the word is a careful label, not a cartoon.

突頜的（下顎比臉的其他部位往前突出）