American English

Definition of radius noun from the Oxford Advanced American Dictionary



    (pl. radii
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  1. 1a straight line between the center of a circle and any point on its outer edge; the length of this line compare diameter
  2. 2a round area that covers the distance mentioned from a central point They deliver to within a 5-mile radius of the store. Doctors wish to examine everyone living within a 10-mile radius of the factory.
  3. 3(anatomy) the shorter bone of the two bones in the lower part of the arm between the elbow and the wrist, on the same side as the thumb see also ulna
See the Oxford Advanced Learner's Dictionary entry: radius