Definition:Circle/Diameter

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.

Also see

• Definition:Diameter of Conic Section:
  • Definition:Diameter of Ellipse
  • Definition:Diameter of Parabola
  • Definition:Diameter of Hyperbola

Linguistic Note

There are two adjectival forms of diameter:

Diametral

Diametral means:

located on or forming a diameter.

Diametrical

Diametrical means:

relating to or along a diameter.

Sources

• 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): diameter: 1.
• 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): diameter: 1.
• 2014: Christopher Clapham and James Nicholson: The Concise Oxford Dictionary of Mathematics (5th ed.) ... (previous) ... (next): diameter