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.
- Mathematics A straight line segment passing through the center of a figure, especially of a circle or sphere, and terminating at the periphery.
- Mathematics The length of such a segment.
- Thickness or width.
- A unit for measuring the magnifying power of a microscope lens or telescope, equal to the number of times an object's linear dimensions are apparently increased.