ra·​di·​us | \ ˈrā-dē-əs How to pronounce radius (audio) \
plural radii\ ˈrā-​dē-​ˌī How to pronounce radius (audio) \ 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.
See More
Recent Examples on the Web Pitts has exquisite size at 6 foot 6, 240 pounds and the catch radius teams crave for in a tight end along with sure hands and the ability to adjust his body to make contested catches like a wide receiver. Omar Kelly, sun-sentinel.com, "Kelly: A look at the 2021 NFL draft’s top-25 talents | Analysis," 24 Apr. 2021 This is because the volume depends on the length and the square of the radius. Rhett Allain, Wired, "How Strong Is King Kong? And Could He Even Stand Up?," 7 Apr. 2021 The measurement, which was presented at the virtual Lunar and Planetary Science Conference this week, suggests that the radius of the Martian core is around 1,810 to 1,860 kilometers, according to the scientific journal Nature. Julia Musto, Fox News, "Mars is first inner planet after Earth to have core measured," 19 Mar. 2021 The measurement suggests that the radius of the Martian core is 1,810 to 1,860 kilometres, roughly half that of Earth’s. David Bressan, Forbes, "Mars Becomes The First Inner Planet After Earth To Have Its Core Measured," 18 Mar. 2021 The only time that the radius of the Earth is of any importance is while determining positions for near-Earth objects such as the moon. Curtis Roelle, baltimoresun.com/maryland/carroll, "Star Points: Celestial coordinate system helps maps out the sky," 6 Mar. 2021 The free website allows users to enter their Zip code and then adjust the search radius to find a vaccine. Leada Gore | Lgore@al.com, al, "Find COVID vaccine by Zip code via new CDC website," 26 Feb. 2021 Owners of businesses within the blast radius got a first look at damage Tuesday after the buildings had been blocked off behind an investigative perimeter since Friday. Jay Cannon, USA TODAY, "Motive in Nashville explosion still unclear as business owners return to 'eerie' site; Warner's girlfriend warned of bomb-making in 2019," 31 Dec. 2020 With an investigation led by federal officials still underway, Nashville police chief John Drake told reporters in an evening press conference that tissue believed to be human remains was found within the blast radius. Mica Soellner, Washington Examiner, "Nashville RV explosion: Possible human remains found in vicinity, and mayor issues state of civil emergency," 25 Dec. 2020

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.

See More

First Known Use of radius

1578, in the meaning defined at sense 1

History and Etymology for radius

Latin, ray, radius

Keep scrolling for more

Learn More about radius

Statistics for radius

Last Updated

28 Apr 2021

Cite this Entry

“Radius.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/radius. Accessed 7 May. 2021.

Style: MLA
MLACheck Mark Icon ChicagoCheck Mark Icon APACheck Mark Icon Merriam-WebsterCheck Mark Icon

Keep scrolling for more

More Definitions for radius



English Language Learners Definition of radius

technical : 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 How to pronounce radius (audio) \
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 How to pronounce radius (audio) \
plural radii\ -​ē-​ˌī How to pronounce radius (audio) \ 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

Keep scrolling for more

Comments on radius

What made you want to look up radius? Please tell us where you read or heard it (including the quote, if possible).


Test Your Vocabulary

Star Wars Words Quiz

  • cu jedi training
  • The bounty portion of bounty hunters (such as Boba Fett) comes from a Latin word meaning
How Strong Is Your Vocabulary?

Test your vocabulary with our 10-question quiz!

Universal Daily Crossword

A daily challenge for crossword fanatics.

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!