radius

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noun ra·di·us \ˈrā-dē-əs\

Definition of radius

plural

radii

play \-dē-ˌī\ also

radiuses

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 fishesb : the third and usually largest vein of an insect's wing
3a : the length of a radius a truck with a short turning radiusb : the circular area defined by a stated radiusc : a bounded or circumscribed area
4 : a radial part
5 : the distance from a center line or point to an axis of rotation

See radius defined for English-language learners

See radius defined for kids

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 of radius from the Web

A conch blown on a summer morning about 1000 years ago at Pueblo Bonito, a village located in the middle of the canyon, would be heard throughout downtown Chaco within a radius of almost 1.5 kilometers, the scientists report.

— giorgia guglielmi, Science | AAAS, "This conch shell trumpet would be heard far and wide in the ancient world," 14 July 2017
Residents within a 1-mile radius of the spill, about 4 miles southwest of Bastrop, Texas, were evacuated.

— laura blewitt, Bloomberg.com, "Texas Oil Spill Shuts Pipe, Routs Residents Outside Austin," 13 July 2017
Locally grown and foraged ingredients sourced from within a 40-mile radius take center stage as diners are treated to wild foods such as ramps and garden nasturtium.

— sylvie morgan brown, Bon Appetit, "A Weekender's Guide to Eating, Drinking, and Shopping in the Hudson Valley," 10 July 2017
The office will represent downtown Birmingham, as well as any area within a 20- to 30-mile radius.

— tara massouleh, AL.com, "Movies, music, and artisan iced tea: what's happening in Birmingham this month," 7 July 2017
The aircraft, called Aquila, aims to provide Internet access to remote corners of the world by transmitting a signal that can be received on the ground within a 60-mile radius.

— garrett mitchell, USA TODAY, "Facebook's Internet-delivering drone takes flight," 30 June 2017
All of the artists famous at that time were located within a 10-block radius of each other.

— susan dunne, courant.com, "NBMAA's Largest Exhibit Shows Off 'L.A. Cool' Artists," 29 June 2017
There are 8.4 million people living with a 50-mile radius of the plant, which is in the process of being decommissioned.

— rob nikolewski, sandiegouniontribune.com, "House panel passes bill that resurrects sending nuclear waste to Yucca Mountain," 28 June 2017
Within a 2-mile radius of the project site is Liberty Center, the Liberty Township campus of Cincinnati Children’s Hospital Medical Center, Christ Hospital Medical Center, the bus compound for the Lakota schools, and Lakota East High School.

— sue kiesewetter, Cincinnati.com, "Yearlong Yankee Road project starts July 5," 27 June 2017

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.

Origin and Etymology of radius

Latin, ray, radius

NEW! Time Traveler

First Known Use: 1578

See Words from the same year

Other Mathematics and Statistics Terms

abscissa, denominator, divisor, equilateral, exponent, hypotenuse, logarithm, oblique, radii, rhomb

RADIUS Defined for English Language Learners

radius

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noun

Definition of radius for English Language Learners

: 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

RADIUS Defined for Kids

radius

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noun ra·di·us \ˈrā-dē-əs\

Definition of radius for Students

plural

radii

\-dē-ˌī\

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

Medical Dictionary

radius

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noun ra·di·us \ˈrād-ē-əs\

Medical Definition of radius

plural

radii

\-ē-ˌī\play 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