Definition of pachycephalosaurid in US English:

pachycephalosaurid

noun

  • A bipedal herbivorous ornithischian dinosaur of the late Cretaceous genus Pachycephalosaurus or a related genus of the family Pachycephalosauridae (or infraorder Pachycephalosauria), characterized by a thickened, dome-like skull.

adjective

  • Of, relating to, or designating dinosaurs of the genus Pachycephalosaurus and related genera.

Origin

1970s; earliest use found in Discovery. From Pachycephalosaurus + -id. Compare scientific Latin Pachycephalosauridae, family name.