Going through a specification sheet for an engineering device, I glanced upon this phrase:
...the angular scanning range of the device is a semicircle of 300 degrees...
A semicircle is usually defined as a proper half of a circle - in mathematical terms a circle of angle 180 degrees. Clearly 300 degrees is more than a half, it is closer to being 5/6th of a circle. Is it grammatically correct to refer to non-full circles as a "semicircle", even though they are not exactly a half-circle.