# Can “semicircle” be used to refer to a part-circle that is not a exact half-circle?

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.

The answer by Steven is correct, you cannot use semicircle in this case.
Here are some alternatives I would use:

the angular scanning range of the device is an arc of 300 degrees…

Or if we want to give a sense of an area being scanned:

the angular scanning range of the device is a circular sector of 300 degrees…

Here’s the definition of circular sector

Or simply:

the angular scanning range of the device is 300 degrees…

I think this is the most technically accurate one. The angular range should be described as an angle, hence measured in degrees (or rads).