diameter
n. C / Un. the length of a straight line that goes from one side of a circle to the other, passing through the center. You use this to measure how wide a round object is.
n. a straight line passing from side to side through the centre of a body or figure, especially a circle or sphere. The term also refers to the length of such a line.
The diameter of the circle is ten centimeters.
Measure the diameter of the pipe to ensure the new connector fits tightly.
Astronomers calculated the planet's diameter by observing the duration of its transit across the face of its host star.
From Old French diametre (French diamètre), from Latin diametros, from Ancient Greek διάμετρος (diámetros) (γραμμή (grammḗ)) (diametros grammē, “line measuring across”), from διά (diá, “across”) + μέτρον (métron, “measure”). By surface analysis, dia- + -meter.