pach·y·ceph·a·lo·saur·us 
(păk′ĭ-sĕf′ə-lə-sôrəs)
(păk′ĭ-sĕf′ə-lə-sôrəs)n.
A large pachycephalosaurian dinosaur of the genus Pachycephalosaurus, having a thick domed skull with bony knobs and a long tail. Also called pachycephalosaur.
[New Latin Pachycephalosaurus, genus name : Greek pakhus, thick + Greek kephalē, head; see ghebh-el- in the Appendix of Indo-European roots + Greek sauros, lizard.]