Definition

1. Noun:
   • A straight line segment passing through the center of a circle or sphere, connecting two points on its circumference or surface. This is the primary geometric definition.
   • The length of such a line segment. This refers to the specific measurement.

Usage

• The diameter is a fundamental measurement for circles and spheres. It is always twice the length of the radius.
• It is used in mathematical formulas, engineering, manufacturing, and everyday descriptions of size.
• When specifying magnification (e.g., for a lens), "diameters" indicates how many times larger an image appears compared to its original size.

Examples

• Noun (Geometric Line):
  • Draw the diameter of the circle from point A to point B.
  • The axis of a sphere is any diameter.
• Noun (Measurement):
  • The diameter of the pipe is exactly 10 centimeters.
  • Calculate the circle's area using its diameter.

Advanced Usage

• "In diameter": A common phrase used to specify the measured length across a circular object.
  • The tree trunk was over two meters in diameter.
• Used in magnification: Expressing linear magnification, often for lenses or optical devices.
  • The telescope lens offers a magnification of 30 diameters.

Variants and Related Words

• Radius (n): The distance from the center to the circumference of a circle or sphere; exactly half the diameter.
• Diameteral (adj): Pertaining to or along a diameter. (Less common variant of 'diametral').
• Diametral (adj): Of, relating to, or constituting a diameter.
• Diametrically (adv): Completely, directly, as in opposite ends of a diameter. Often used in the phrase "diametrically opposed."

Synonyms

• Width (when referring to the measurement across a circular object).
• Breadth (similar to width, for the measurement across).

Antonyms

• Radius (specifically as half the measure, not an opposite line).

Related Phrases and Idioms

• Diametrically opposed: Being in complete, direct opposition, as if at opposite ends of a diameter.
  • Their political views are diametrically opposed.

Noun

1. 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)
2. the length of a straight line passing through the center of a circle and connecting two points on the circumference