ra·di·us | \ˈrā-dē-əs \
plural radii\ˈrā-dē-ˌī \ also radiuses

Definition of radius 

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

2a : 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

3a : 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.
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Recent Examples on the Web

Keep an eye on third-round pick Michael Gallup, who could become one of Prescott's favorites given his wide catch radius and penchant for creating separation with precise route running. Michael Middlehurst-schwartz, USA TODAY, "Cowboys training camp questions: Who steps up at receiver for Dak Prescott?," 12 July 2018 The large space features indoor and outdoor seating, a sunny spot to feast on the grub sourced from within a 10-mile radius. Sam Dangremond, Town & Country, "T&C Travel Guide: Napa Valley and Sonoma County, California," 9 July 2018 In addition to airport pickup, the inn provides courtesy transportation within a 5-mile radius of the hotel throughout your stay. Joanne Dibona, sandiegouniontribune.com, "Boise trip is a capital idea," 5 July 2018 The Rite Aid at 510 E. Baltimore Pike in Media, Delaware County, was out of Shingrix, but eight other Rite Aids within a 10-mile radius still had at least a few doses available, a pharmacist said. Mari A. Schaefer, Philly.com, "Looking for the new shingles vaccine Shingrix? Not all Philadelphia pharmacies have it," 29 June 2018 Coaches were impressed with his attitude during OTAs and minicamp, and his catch radius enabled more than a couple one-hand catches that caught everyone’s attention. Albert Breer, SI.com, "Everybody Wants to Talk to Lincoln Riley," 25 June 2018 Michael Tuohy, then-chef at Golden 1 Center, brought Diaz to Sacramento just two months after the NFL championship game, and Diaz was able to source 90 percent of ingredients within a 150-mile radius of Golden 1. Cathie Anderson, sacbee, "Hospital food gets a farm-to-fork makeover from UC Davis Medical Center's new chef," 18 June 2018 About 90 percent of the wine grapes in Texas are grown within a 100-mile radius of Lubbock, many in fields that used to yield less-profitable cotton. Dan Fellner, azcentral, "Why Lubbock, TX, is hot: Texas Tech, Buddy Holly and wine," 13 June 2018 Park district officials have said the financial problems are systemic due to declining revenues and high operating costs, in addition to 21 other courses being within a 10-mile radius. Daniel I. Dorfman, chicagotribune.com, "The Lake Bluff Golf Club's future is in doubt, unless private funds can be raised to keep it running," 6 June 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'radius.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of radius

1578, in the meaning defined at sense 1

History and Etymology for radius

Latin, ray, radius

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Statistics for radius

Last Updated

5 Oct 2018

Look-up Popularity

Time Traveler for radius

The first known use of radius was in 1578

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English Language Learners Definition of radius

: a straight line from the center of a circle or sphere to any point on the outer edge; also : the length of this line

: an area that goes outward in all directions from a particular place

medical : the bone in the lower part of your arm on the same side as your thumb


ra·di·us | \ˈrā-dē-əs \
plural radii\-dē-ˌī \

Kids Definition of radius

1 : a straight line extending from the center of a circle to the outside edge or from the center of a sphere to the surface

2 : an area that extends in all directions from a place Most students live within a radius of five miles from the school.

3 : the bone on the thumb side of the arm between the wrist and the elbow


ra·di·us | \ˈrād-ē-əs \
plural radii\-ē-ˌī \ also radiuses

Medical Definition of radius 

: 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

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More from Merriam-Webster on radius

Spanish Central: Translation of radius

Nglish: Translation of radius for Spanish Speakers

Britannica English: Translation of radius for Arabic Speakers

Britannica.com: Encyclopedia article about radius

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