a straight line between the centre of a circle and any point on its outer edge; the length of this line 半徑（長度） 
a round area that covers the distance mentioned from a central point 半徑範圍；周圍 - within a… radius
They deliver to within a 5-mile radius of the store. 他們給店鋪方圓 5 英裏内送貨上門。 Doctors wish to examine everyone living within a 10-mile radius of the factory. 醫生希望對工廠方圓10英裏内的每個人進行檢查。
- within a… radius
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anatomy 解剖學 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’.