1. a straight line passing through the center of a circle or sphere and connecting two points on the circumference
Usage: geometry
2. the length of such a line; the width of a circular object measured through its center

Examples

• The diameter of the circle is 10 inches.
• She measured the diameter of the pipe with a ruler.
• The moon’s diameter is about one-fourth that of Earth.
• Draw a line across the diameter of the circle.
• The tree trunk has a diameter of three feet.
• Calculate the area using the circle’s diameter.
• The diameter divides the circle into two equal halves.