1) Arc 2) Cee 3) Curve 4) Hemicycle 1) Array of trucks 2) Elementary geometry 3) Half a ring 4) Hemicycle 5) Plane figure 6) Two-dimensional figure 7) Typical protractor 8) Zero halved 
In mathematics (and more specifically geometry), a semicircle is a one-dimensional locus of points that forms half of a circle. The full arc of a semicircle always measures 180° (equivalently, {pi} radians, or a half-turn). It has only one line of symmetry (reflection symmetry). In non-technical usage, the term `semicircle` is sometimes used to.....
• (n.) An instrument for measuring angles. • (n.) A semicircumference. • (n.) A body in the form of half of a circle, or half of a circumference. • (n.) The half of a circle; the part of a circle bounded by its diameter and half of its circumference.
Sem'i·cir`cle noun 1. (a) The half of a circle; the part of a circle bounded by its diameter and half of its circumference. (b) A semicircumference. 2. A body in the form of half of a circle, or half of a circumference. 3. An instrument for measuring angles. ...
A semicircle is half a circle.
[n] - a plane figure with the shape of half a circle
hemicycle noun a plane figure with the shape of half a circle