In
geometry, a
diameter of a
circle is any straight
line segment that passes through the center of the circle and whose endpoints lie on the circle. It can also be defined as the longest
chord of the circle. Both definitions are also valid for the diameter of a
sphere. The word "diameter" is derived from
Greek διάμετρος (
diametros), "diameter of a circle", from
δια- (
dia-), "across, through" +
μέτρον (
metron), "measure". It is often abbreviated
DIA,
dia,
d, or
⌀.