Main Entry:

ra·di·us

Pronunciation:

\ˈrā-dē-əs\

Function:

noun

Inflected Form(s):

plural ra·dii \-dē-ˌī\ also ra·di·us·es

Etymology:

Latin, ray, radius

Date:

circa 1611

1: a line segment extending from the center of a circle or sphere to the circumference or bounding surface2 a: the bone on the thumb side of the human forearm ; also : a corresponding part of vertebrates above fishes b: the third and usually largest vein of an insect's wing3 a: the length of a radius <a truck with a short turning radius> b: the circular area defined by a stated radius c: a bounded or circumscribed area4: a radial part5: the distance from a center line or point to an axis of rotation