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Etymology-wise, what part of a circle is a beam of light?

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Answer: the radius

The straight-line distance from the centre of a circle to its circumference is called the radius, which means "beam of light" in Latin.


As worded, I think this question is bad. I suggest, "Etymologically speaking, what part of a circle is a beam of light?" Except in an etymological sense, no part of a circle is a beam of light. [Mootguy: Good point. I'll change it.]
derek at

Actually, the radius isn't PART of a circle at all, it's a characteristic of a circle. Perhaps "one radian" would be a more appropriate answer, since this actually represents PART of a circle.

[Mootguy: An analogy: We know that Bob's arm is part of Bob. But is Bob's height part of Bob? Maybe "aspect" is a better word. Thus the questions becomes: "Etymology-wise, what aspect of a circle is a ray of light?"]

The wording is a bit tricky since, as you point out, the radius is not part of a circle in the same way that Bob's arm is a part of Bob.

The latter is a constituent part: if you removed it, part of Bob would be missing. However, the radius is a mental extrapolation; remove it from the circle and the circle would still be there.

Now there's a good piss-you-off moot question for you: Is the circle's radius part of the circle? That question homes in on the meaning of part, a word that we all thought we knew the meaning of before this question.(I would also change "the circle" to "a circle.") [Mootguy: I agree. Done. I'll try your question out at the next live MooT game we have in Vancouver.]
jacko at

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