hēmĭcyclium
hēmĭcyclium, ĭi, n., = ἡμικύκλιον, a half-circle, semicircle, Vitr. 9, 8, 5; Plin. Ep. 5, 6, 33.— In partic. A semicircular recess, with seats, Cic. Lael. 1, 2; Sid. Ep. 2, 2.— A semicircular public place furnished with rows of seats for learned discussions, Suet. Gramm. 17.— A semicircular kind of sundial, Vitr. 9, 8, 1.