1) Bandshell 2) Plane figure 3) Semicircle 4) Two-dimensional figure 1) Semicircle 
• (n.) A semicircular place, as a semicircular arena, or room, or part of a room. • (n.) A half circle; a semicircle.
Hem'i·cy`cle noun [ Latin hemicyclus , Greek ...; ... + ....] 1. A half circle; a semicircle. 2. A semicircular place, as a semicircular arena, or room, or part of a room. « The collections will be displayed in the hemicycle of the central pavilion.» Lon...
The group of columns, arranged in a semicircular formation, that divide the east end of a choir from the ambulatory.