- Geometry.
- a straight line passing through the center of a circle or sphere and meeting the circumference or surface at each end.
- a straight line passing from side to side of any figure or body, through its center.
- the length of such a line.
- the width of a circular or cylindrical object.
- a straight line connecting the centre of a geometric figure, esp a circle or sphere, with two points on the perimeter or surface
- the length of such a line
- the thickness of something, esp with circular cross section
