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.
Recent Examples on the Web Authorities sent out a reverse 911 alert asking people within a half-mile radius of the hotel to avoid the area. Joe Taschler, Milwaukee Journal Sentinel, 29 Apr. 2022 This is coffee country, so guests can visit local growers and take part in tastings; rooms are equipped with kettles and coffeemakers from trendy brand Fellow, along with beans picked within a five-mile radius of the hotel. Travel + Leisure, 12 Apr. 2022 Built in 2019, Publix occupies most of the shopping center and is the grocery chain’s only location within a four-mile radius. William Thornton | Wthornton@al.com, al, 22 Mar. 2022 Delivery must be within a three-mile radius of St. Brendan. Carol Kovach, cleveland, 1 Mar. 2022 Within a couple mile radius, 28 others donated, many $100 or more. Washington Post, 10 Feb. 2022 The city opened Winston-Salem Fairgrounds’ education building—at 414 Deacon Blvd.—for people within a one-mile radius of the fire’s location. Allison Prang, WSJ, 1 Feb. 2022 Mayo said about 2,500 homes are within a mile radius of the plant and that about 6,500 people living within the area have been advised to evacuate. Bill Hutchinson, ABC News, 1 Feb. 2022 Authorities drove through neighborhoods and knocked on doors asking residents to leave within a one-mile radius of the Winston Weaver Company fertilizer plant on the north side of Winston-Salem, where the fire started Monday night. Tom Foreman Jr. And Ben Finley, Anchorage Daily News, 1 Feb. 2022 See More

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.

First Known Use of radius

1578, in the meaning defined at sense 1

History and Etymology for radius

Latin, ray, radius

Learn More About radius

Dictionary Entries Near radius

radium vermilion


radius bar

See More Nearby Entries 

Statistics for radius

Last Updated

10 May 2022

Cite this Entry

“Radius.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/radius. Accessed 21 May. 2022.

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More Definitions for radius


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


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