radius
n. countablen. the distance from the center of a circle to its outside edge. It also means the area within a certain distance of a central point.
n. a straight line from the centre to the circumference of a circle or sphere. Also used to describe a circular area of a specified distance from a central point.
The park is within a five-mile radius of my house.
The search party covered every field within a ten-kilometer radius of the missing hiker's last known location.
To calculate the area of the circle, you must first measure the radius and then square that value before multiplying it by pi.
Borrowed from Latin radius (“ray”). Doublet of ray.
The plural form is typically 'radii' in technical or mathematical contexts, though 'radiuses' is occasionally used in general speech.