4

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.

10
  • 9
    I would say the word arc can be used: "an arc of 300 degrees," or perhaps: "the scanning range of the device is an angle of 300 degrees". Commented Mar 13, 2019 at 17:24
  • 4
    No, you can't use it. A semi-circle means half of a circle.
    – Ubi.B
    Commented Mar 13, 2019 at 17:31
  • I presume it is clear from context that you are talking about geometric angle measure, not temperature. Thus, I would get rid of the "angular scanning range" as completely superfluous non-information. Instead, you may want to add actual information, like that it is scanning range in horizontal (or vertical) plane. Or is a sphere? Or half-sphere? Look at it from the point of view of a user of the device.
    – Rusty Core
    Commented Mar 13, 2019 at 21:11
  • 3
    It is 5/6 of a circle.
    – user207421
    Commented Mar 13, 2019 at 21:23
  • @WeatherVane The word should needs to be used in "... the word arc can be used," not can. Arc it is, after all.
    – Kris
    Commented Mar 14, 2019 at 8:24

2 Answers 2

3

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).

16

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.

7
  • This might be an unusual opinion, but when I hear "semiannually" I think "probably once every 2 years, but inconsistently so". I'm Australian, in case that's relevant.
    – Clonkex
    Commented Mar 14, 2019 at 3:05
  • 1
    Biannual is the term for something that happens every six months. Not to be confused with biennial which is something that happens every two years.
    – mcalex
    Commented Mar 14, 2019 at 5:53
  • @Clonkex "semi-" means half, and "bi-" (as in bicycle, which is how I remember the difference) means two.
    – RonJohn
    Commented Mar 14, 2019 at 8:10
  • Please read the FAQ. Good Luck.
    – Kris
    Commented Mar 14, 2019 at 8:26
  • @RonJohn I understand that, but that's not how I naturally interpret "semiannually". I only point this out because I may not be alone.
    – Clonkex
    Commented Mar 15, 2019 at 3:55

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.