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

Solution 1:

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).

Solution 2:

In English, the prefix semi- usually means partly, as in semiconscious or semiautomatic.

But it can also mean half, as in semiannually, which always refers to something that happens every half-year (twice yearly).

The word semicircle has a specific defined meaning: a half of a circle or of its circumference. (Source: New Oxford American Dictionary)

So no, semicircle cannot be used to refer to any part of a circle that isn't 180 degrees.