radius

noun

ra·​di·​us ˈrā-dē-əs 

plural radii ˈrā-dē-ˌī  also radiuses

1

: a line segment extending from the center of a circle or sphere to the circumference or bounding surface

2

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 wing

3

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 area

4

: a radial part

5

: the distance from a center line or point to an axis of rotation

Examples of radius in a Sentence

Measure the radius of the circle.

a radius of 10 inches

The new museum is expected to draw people from a wide radius.

There are three restaurants within a one-block radius of our apartment.

Recent Examples on the Web

Once Cohen settled, the team descended like a Nascar pit crew to take his measurements: radius of cranium, distance between eyes, width of nostrils. —Zach Zimmerman, The New Yorker, 23 Dec. 2024

At the epicenter of the trial are 51 men, all who lived within a 30-mile radius of one another. —Saskya Vandoorne, CNN, 19 Dec. 2024

Forty-nine men who, under the cover of darkness, joined him in assaulting her—men identified as nurses and prison guards, firefighters and truck drivers, all living within a 31-mile radius of each other, ranging in age from 27 to 72. —Hayley Maitland, Vogue, 19 Dec. 2024

Little Rest Single Malt Whiskey 2nd Release, Tenmile Distillery ($100) Produced in Wassaic in New York's Hudson Valley, this whiskey utilizes local ingredients found within a 30-mile radius of the distillery’s location when growing conditions in the region allow. —Erik Ofgang, Forbes, 18 Dec. 2024

Word History

Etymology

Latin, ray, radius

First Known Use

1578, in the meaning defined at sense 1

Phrases Containing radius

• radius of curvature
• radius vector

Kids Definition

radius

noun

ra·​di·​us ˈrād-ē-əs 

plural radii -ē-ˌī  also radiuses

1

: the bone on the thumb side of the human forearm

also : a corresponding bone of other vertebrates

2

: a line extending from the center of a circle or sphere to the circumference or surface

3

a

: the length of a radius

b

: a circular area defined by a given radius

deer may wander within a radius of several miles

4

: a radial part or plane

Etymology

from Latin radius "ray, beam, spoke" — related to radiate, radio, ray entry 2

Medical Definition

radius

noun

ra·​di·​us ˈrād-ē-əs 

plural radii -ē-ˌī  also radiuses

: the bone on the thumb side of the human forearm or on the corresponding part of the forelimb of vertebrates above fishes that in humans is movably articulated with the ulna at both ends so as to permit partial rotation about that bone, that bears on its inner aspect somewhat distal to the head a prominence for the insertion of the biceps tendon, and that has the lower end broadened for articulation with the proximal bones of the carpus so that rotation of the radius involves also that of the hand