radius

play

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

2 a :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

3 a :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

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

The system also has created a mobile app called Here to Career, which helps students explore certificates and degrees that are available within a 50-mile radius of their home.

— gary warth, sandiegouniontribune.com, "Community colleges focus more on career education as classes start," 19 Aug. 2017
The program also has expanded the search radius for available vehicles.

— jason laughlin, Philly.com, "Should Philly follow Boston and remake paratransit with ride hailing?," 14 Aug. 2017
Kyle Green kgreen@idahostatesman.com Fitting tens of thousands of visitors and residents in a three-square mile radius is a challenging proposition.

— michael katz, idahostatesman, "Tiny Weiser, Idaho, is an eclipse hot spot. Is it ready for 20,000-plus visitors?," 9 Aug. 2017
Maybe this news will convince Chip and Joanna to finally expand their 40-mile-radius-of-Waco requirement to include more areas of the Lone Star State!

— taysha murtaugh, Country Living, "The Best Place In the Country to Flip Houses Is In Texas—But It's Not Waco," 4 Aug. 2017
Kief, meanwhile, is a versatile player who ran a 4.59 40 during the spring at 6-foot-4, 205 pounds and is described by people at Alabama as a good route runner with good ball skills and a big catch radius.

— matt zenitz, AL.com, "Alabama fall camp position breakdown: Wide receivers," 27 July 2017
Uncle's Hawaiian Grindz uses ingredients that are sourced within a 100-mile radius of the Fallston restaurant, whenever possible, Trabbold said.

— david anderson, The Aegis, "First chef's challenge a hit at Harford Farm Fair," 26 July 2017
The official Xinhua News Agency said glass was blown out of the windows of vehicles and buildings within a wide radius of the shop.

— Bloomberg.com, "Explosion Hits Food Shop in China, Killing 2, Injuring 55," 21 July 2017
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

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

play

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

play

noun ra·di·us \ ˈrād-ē-əs \

medical Definition of radius

plural radii play \-ē-ˌī\ 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