radius

[rey-dee-uhs]

noun

plural

radii, radiuses 

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.

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

plural

radii 

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

During this period, bears dramatically expand their search radius, often pushing deeper into residential areas.

Read more on Los Angeles Times

I pulled out my graph paper and my French curves, which would help me draw curves of different radii.

Read more on Literature

Beyond my own square radius, I have seen an art world that is far less individualistic than those in other major cities — one oriented toward collaboration and joining forces to make something more meaningful.

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SN 2024ggi began as a red supergiant with a mass between 12 and 15 times that of the Sun and a radius 500 times larger.

Read more on Science Daily

Typhoon Fung-wong, a swirling storm with a radius spanning nearly the entirety of the Philippines, reached super typhoon status on Sunday ahead of an expected late-night landfall.

Read more on Barron's