[ θɛ'rapsɪd ]
■ noun Palaeontology a fossil reptile of a large group including the cynodonts, related to the ancestors of mammals.
Origin
early 20th cent.: from mod. L. Therapsida (name of an order), from Gk thēr 'beast' + hapsis , hapsid- 'arch' (referring to the structure of the skull).