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

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
Most of Baton Rouge and south Louisiana were already here, roaming the downtown bars and restaurants and occupying hotels within a 20-mile radius.

— ron higgins, NOLA.com, "LSU is far from panic mode after losing its College World Series opener", 27 June 2017
Villa Creek, Artisan and the other top-notch restaurants sit within a three-block radius of each other in downtown, from Thomas Hill Organics to the fine dining Il Cortile Ristorante.

— tan vinh, The Seattle Times, "New flight makes it easy to explore California’s top-notch Paso Robles wine country", 14 June 2017
That increases to 6 percent within a 3-mile radius of First and Washington streets.

— brenna goth, azcentral, "Phoenix is the nation's 5th largest — but is it a 'real' city?", 11 June 2017
Officers wouldn't be allowed to live in Indiana, and the center of the 30-mile radius is 183rd Street and 80th Avenue, just west of where the police station is located.

— mike nolan, Daily Southtown, "Tinley Park to eliminate residency rule for police", 8 June 2017
Its iron innards take up over 80 percent of its radius, or more than 60 percent of its volume.

— ryan mandelbaum, The Atlantic, "Mercury Is the Inspectah Deck of Planets", 2 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!

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

play

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