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Definition of radius noun from the Oxford Advanced Learner's Dictionary

radius

noun
radius pronunciation English ˈreɪdiəs radius pronunciation American ˈreɪdiəs
plural radii
radii pronunciation English ˈreɪdiaɪ radii pronunciation American ˈreɪdiaɪ
 
1 a straight line between the centre of a circle and any point on its outer edge; the length of this line compare diameter2 a round area that covers the distance mentioned from a central pointThey 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 (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