radius

[ rey-dee-uhs ]

noun

, plural ra·di·i [rey, -dee-ahy], ra·di·us·es.

1. a straight line extending from the center of a circle or sphere to the circumference or surface:

   The radius of a circle is half the diameter.

2. the length of such a line.
3. any radial or radiating part.
4. a circular area having an extent determined by the length of the radius from a given or specified central point:

   every house within a radius of 50 miles.

5. a field or range of operation or influence.
6. extent of possible operation, travel, etc., as under a single supply of fuel:

   the flying radius of an airplane.

7. Anatomy. the bone of the forearm on the thumb side. Compare ulna ( def 1 ).
8. Zoology. a corresponding bone in the forelimb of other vertebrates.
9. Machinery Now Rare. the throw of an eccentric wheel or cam.
10. a rounded corner or edge on a machined or cast piece of metal.
11. Entomology. one of the principal longitudinal veins in the anterior portion of the wing of an insect.

radius

/ ˈreɪdɪəs /

noun

1. a straight line joining the centre of a circle or sphere to any point on the circumference or surface
2. the length of this line, usually denoted by the symbol r
3. the distance from the centre of a regular polygon to a vertex ( long radius ) or the perpendicular distance to a side ( short radius )
4. anatomy the outer and slightly shorter of the two bones of the human forearm, extending from the elbow to the wrist
5. a corresponding bone in other vertebrates
6. any of the veins of an insect's wing
7. a group of ray florets, occurring in such plants as the daisy
8. 1. any radial or radiating part, such as a spoke
   2. ( as modifier )

      a radius arm

9. the lateral displacement of a cam or eccentric wheel
10. a circular area of a size indicated by the length of its radius

    the police stopped every lorry within a radius of four miles

11. the operational limit of a ship, aircraft, etc

radius

/ rā′dē-əs /

, Plural radii rā′dē-ī′

1. A line segment that joins the center of a circle or sphere with any point on the circumference of the circle or the surface of the sphere. It is half the length of the diameter.
2. The shorter and thicker of the two bones of the forearm or the lower portion of the foreleg.
3. See more at skeleton

Word History and Origins

Origin of radius¹

First recorded in 1590–1600; from Latin: “staff, rod, spoke, beam,” originally, “ray”; ray ¹

Word History and Origins

Origin of radius¹

C16: from Latin: rod, ray, spoke

Example Sentences

At this point, solvers like Thanh Nguyen used trigonometry to calculate the inner radius of the annulus, which turned out to be R√3.

From FiveThirtyEight

Not only did Grinin’s team find a value for the charge radius of the proton consistent with the value obtained in muonic hydrogen, they inferred a much more precise value for the Rydberg constant.

From Nautilus

Know your radiusEvery smart device implements its geofencing radius a little differently.

From Popular-Science

Through our network of centrally located fulfillment centers we are able to service customers in a small delivery radius.

From TechCrunch

There are a couple of ways to measure a proton's charge radius.

From Ars Technica

By “the Internet,” they meant the people within a seven-cubicle radius of the person who wrote that blog post.

From The Daily Beast

Soon even the closest spectators, right at the edge of my empty radius, turned and looked at me.

From The Daily Beast

Another requirement was that the Colombian National Police would not be permitted within a 12-mile radius of his prison.

From The Daily Beast

In 2012, FIS announced a new requirement increasing the minimum turn radius of GS skis by eight meters.

From The Daily Beast

These were then spread over a 300-mile radius, covered in ravines, gorges and pine forests.

From The Daily Beast

And from my roost I could note the passing of anything bigger than a buffalo yearling, within a radius of at least six miles.

From Project Gutenberg

Some of them, stronger than others, sent roots for a radius of a hundred miles, others for a few leagues and no more.

From Project Gutenberg

General Steuben observing the large radius of camp concluded that Cornwallis' entire force was across the river.

From Project Gutenberg

There are a good many neighbours within a radius of five miles; the trains to town are not all that could be wished.

From Project Gutenberg

A very dense fog enveloped everything, confining the view of surrounding objects to a radius of about fifty yards.

From Project Gutenberg