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

The team looked at such factors as size, the occurrence of lawn, plant and tree growth, artificial light sources and green in the surroundings of the location within a 1,000 meter radius.

From Science Daily

The team's artificial intelligence algorithms combined with a headphone prototype allow the wearer to hear people speaking within a bubble with a programmable radius of 3 to 6 feet.

From Science Daily

The plants are considered “hyper-local” because they are grown from seeds that were collected within a five-mile radius of the structure, Rock said.

From Los Angeles Times

“The heavy blast radius kills and maims civilians nearby”, he said, in reference to Israeli air strikes.

From BBC

My partner and I, our life is pretty tight — like a 60-mile radius between New York and New Jersey.

From Los Angeles Times