# Definition:Circle/Diameter

< Definition:Circle(Redirected from Definition:Diameter of Circle)

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## Definition

In the words of Euclid:

*A***diameter of the circle**is any straight line drawn through the center and terminated in both directions by the circumference of the circle, and such a straight line also bisects the center.

(*The Elements*: Book $\text{I}$: Definition $17$)

In the above diagram, the line $CD$ is a **diameter**.