a straight line between the centre of a circle and any point on its outer edge; the length of this line 半径（长度） 
a round area that covers the distance mentioned from a central point 半径范围；周围 - within a… radius
They deliver to within a 5-mile radius of the store. 他们给店铺方圆 5 英里内送货上门。 Doctors wish to examine everyone living within a 10-mile radius of the factory. 医生希望对工厂方圆10英里内的每个人进行检查。
- within a… radius
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anatomy 解剖学 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 桡骨 
Word Originlate 16th cent. (in sense (3)): from Latin, literally ‘staff, spoke, ray’.