/theuh rap"sid/ , n.
1. any of various groups of mammallike reptiles of the extinct order Therapsida, inhabiting all continents from mid-Permian to late Triassic times, some of which were probably warm-blooded and directly ancestral to mammals.
adj.
2. of or pertaining to the Therapsida.
[ Therapsida (1905), equiv. to Gk ther- (s. of thér wild beast) + apsid- (s. of apsís arch, vault, referring to the temporal arch of the skull) + NL -a neut. pl. ending (see -A 1 ) ]