Learner's definition of RADIUS
1 technical : a straight line from the center of a circle or sphere to any point on the outer edgealso : the length of this line 2 : an area that goes outward in all directions from a particular place
The new museum is expected to draw people from a wide radius.
More than 100,000 students live within a 10-mile radius of the university. [=within 10 miles of the university]
There are three restaurants within a one-block radius of our apartment.
3 medical : the bone in the lower part of your arm on the same side as your thumb