diameter -
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)
straight line a line traced by a point traveling in a constant direction; a line of zero curvature; "the shortest distance between two points is a straight line"
A diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle. The word "diameter" derives from Greek διάμετρος (diametros), "diagonal of a circle", from δια- (dia-), "across, through" + μέτρον (metron), "a measure").
OmegaWiki Dictionary
Ω
diameter Distance between the intersections of a circle with a straight line through its center