Longman Dictionary of Contemporary English homepage

Date: 1500-1600
Language: Latin
Origin: 'ray, radius'

radius

noun
     
Related topics: Human, Maths, Measurement
ra‧di‧us plural radii [countable]
1TM the distance from the centre to the edge of a circle, or a line drawn from the centre to the edge [↪ diameter]
2TM an area that covers a particular distance in all directions from a central point:
The shock of the explosion was felt over a radius of forty miles.
within a 10-mile/200-metre etc radius
There are more than a dozen golf courses within a 15-mile radius of St Andrews.
3 technicalHBH the outer bone of the lower part of your arm

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