the linear extent in space from one end to the other; the longest dimension of something that is fixed in place

the length of a straight line passing through the center of a circle and connecting two points on the circumference

the apparent radius of a celestial body when viewed as a disc from the earth

the radius of the circle of curvature; the absolute value of the reciprocal of the curvature of a curve at a given point

In a regular polygon, a line segment from the center to the midpoint of one of its sides.

the length of a straight line passing through the center of a circle and connecting two points on the circumference