If you're a detective working a crime investigation, you might be told to "search over a one-mile radius," meaning, scope out everything that's within one mile of the crime scene.

The radius of a circle is the distance from its center to the circumference, and if you are working on your geometry homework, or designing anything circular, you'll be writing down a little "r" quite frequently, to stand for "radius." It's also the name of one of the bones in your forearm.

Definitions of radius
  1. noun
    a straight line from the center to the perimeter of a circle (or from the center to the surface of a sphere)
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    type of:
    straight line
    a line traced by a point traveling in a constant direction; a line of zero curvature
  2. noun
    support consisting of a radial member of a wheel joining the hub to the rim
    synonyms: spoke, wheel spoke
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    type of:
    any device that bears the weight of another thing
  3. noun
    the length of a line segment between the center and circumference of a circle or sphere
    synonyms: r
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    the apparent radius of a celestial body when viewed as a disc from the earth
    radius of curvature
    the radius of the circle of curvature; the absolute value of the reciprocal of the curvature of a curve at a given point
    type of:
    the linear extent in space from one end to the other; the longest dimension of something that is fixed in place
  4. noun
    a circular region whose area is indicated by the length of its radius
    “they located it within a radius of 2 miles”
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    type of:
    part, region
    the extended spatial location of something
  5. noun
    the outer and slightly shorter of the two bones of the human forearm
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    type of:
    arm bone
    a bone in the arm
Word Family