Radius

Part of speech: noun

Pronunciation: /ˈɹeɪ.di.əs/

Definitions

1. A straight line connecting the center of a circle or sphere to its boundary while also denoting one of the two long bones in the forearm on the thumb side
2. A line segment that reaches from the center to the circumference of a circle or sphere while also referring to one of the two bones located on the thumb side of the forearm
3. The length measured from the midpoint of a circle or sphere to any point on its perimeter or surface ; one of the two primary bones found on the thumb side of the forearm

Etymology: Latin "radius" originally meant a staff, rod, or spoke, and also a ray of light, which is why the English word has a doublet: "ray" came to English through French, while "radius" was taken straight from Latin. The two words are cousins that split apart in the ordinary flow of speech, one becoming a common everyday word for a beam of light and the other staying closer to its Latin form. The geometric sense grew from the image of a spoke. A line running from the centre of a wheel to its rim looks like a rod projecting outward, and the same picture works for any circle or sphere, so the measurement of that spoke gave the word its mathematical meaning. The anatomical sense is a separate application of the same Latin word, referring to the bone on the thumb side of the forearm. It takes its name from the way that bone rotates around the other forearm bone, a movement that resembles a spoke turning within a wheel.

Synonyms: distance, line, segment