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Meaning & use

radius

noun·Academicmathematics

Last updated

UK/ˈreɪdiəs/
US/ˈreɪdiəs/

Meanings

  1. nouncountablemathematics

    A straight line from the center of a circle to its edge, or its length.

    Grammar: Plural radii or radiuses.

    Patterns

    • the radius of a circle

    The circle has a radius of five centimeters.

    Draw a radius to the edge.

    Double the radius to find the diameter.

  2. nouncountable

    The area within a certain distance of a point.

    Grammar: Often within a radius of.

    Patterns

    • within a radius of something

    No shops are within a ten-mile radius.

    Police searched a one-mile radius.

  3. nouncountablemedical

    The shorter bone of the forearm on the thumb side.

    Grammar: Anatomy.

    He broke his radius in the fall.

Word forms

pluralradii
pluralradiuses

Common combinations

within a radius
Within a radius.
radius of a circle
The radius of a circle.
search radius
Search radius.
mile radius
A five-mile radius.

Synonyms and how they differ

range
General reach.
scope
Extent.

Word family

radial adjective
of radii
diameter noun
twice the radius

Commonly confused: radius or diameter?

radius vs diameter

The diameter goes across the whole circle.

Practice

If a circle's diameter is 10 cm, its radius is:

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