hemicycle(n = noun.shape) semicircle - a plane figure with the shape of half a circle;
is a kind of plane figure, two-dimensional figure

1.  A half circle; a semicircle. [1913 Webster]

2.  A semicircular place, as a semicircular arena, or room, or part of a room. [1913 Webster]
"The collections will be displayed in the hemicycle of the central pavilion." [1913 Webster]

hemicycle, n. a semicircular figure.