the length of a straight line passing through the center of a circle and connecting two points on the circumference
source: WordNet 3.0
a straight line connecting the center of a circle with two points on its perimeter (or the center of a sphere with two points on its surface)
source: WordNet 3.0
Any right line passing through the center of a figure or body, as a circle, conic section, sphere, cube, etc., and terminated by the opposite boundaries; a straight line which bisects a system of parallel chords drawn in a curve.
