Lewis Short
(adjective) : sēmĭ-circŭlus, a, um
* 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.
Charlton T. Lewis, Charles Short, A Latin Dictionary