sēmĭ-circŭlus — Lewis & Short
sēmĭ-circŭlus, a, um, adj.,
I semicircular:
ager,Col. 5, 2, 8.—Hence, subst.: sēmĭ-circŭlus, i, m., a half-circle, semicircle (syn. semiorbis):
uncus in semicirculi speciem,Cels. 7, 26, 2:
ager,i. e. semicircular, Col. 5, 2, 8.