# diameter

/daɪˈæmətɝ/ (US) · /daɪˈæmɪtɐ/ (UK)

Source: https://englishreference.com/word/diameter
Updated: 2026-06-19

## Senses

### 1. distance across a circle

noun · CEFR B1

the length of a straight line that goes from one side of a circle to the other, passing through the center.

For teachers: the length of a straight line segment passing through the center of a figure, especially a circle or sphere, and terminating at the periphery.

- The pipe has a diameter of ten centimeters, so it should fit perfectly.
- To calculate the circumference accurately, the engineer first measured the inner diameter of the cylinder using a digital caliper.

### 2. the line itself

noun · CEFR B2

a straight line that divides a circle into two equal halves by passing through the middle.

For teachers: a chord that passes through the center of a circle or sphere.

- Draw a diameter across the circle to show where to cut the paper.
- The geometry problem required students to construct a diameter that was perpendicular to the given chord.

### 3. maximum distance in a space

noun · CEFR C2 · Technical

the largest possible distance between any two points in a specific area or shape.

For teachers: the maximum distance between any two points in a metric space or the maximum eccentricity over all vertices in a graph.

- The diameter of this network is small, meaning any two points are closely connected.
- In graph theory, the diameter of a graph is defined as the greatest distance between any pair of vertices.

Usage: Used primarily in advanced mathematics, topology, and graph theory.

## Examples

- The diameter of the circle is ten centimeters.
- Measure the diameter of the pipe to ensure the new connector fits tightly.
- Astronomers calculated the planet's diameter by observing the duration of its transit across the face of its host star.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.