radius
noun · verb
Simple meaning
The length of a line segment between the center and circumference of a circle or sphere.
Pronunciation
Say it like this:
raydeeuhsSay the bold part a little louder.
IPA pronunciation (US)
ˈɹeɪdiəs
This word is pronounced essentially the same in American and British English, so one transcription covers both.
IPA (International Phonetic Alphabet) is a standard way of writing speech sounds.
Definition
Everyday modern meanings first, grouped by part of speech.
noun
geometry
The length of a line segment between the center and circumference of a circle or sphere
“The radius of the circle was exactly five centimeters long.”
geometry
A straight line from the center to the perimeter of a circle (or from the center to the surface of a sphere)
geometry
A line segment between any point of a circle or sphere and its center.
geometry
The length of this line segment.
anatomy
The long bone in the forearm, on the side of the thumb.
Anything resembling a radius, such as the spoke of a wheel, the movable arm of a sextant, or one of the radiating lines of a spider's web.
verb
transitive
To give a rounded edge to.
Word at a Glance
- Difficulty
- B1 · Intermediate
- Frequency
- Common
- Typical Use
- Everyday English
Word Aura™
How this word commonly comes across.
Aura for this meaning
This meaning: The length of a line segment between the center and circumference of a circle or sphere
Used this way, radius is a specialist word that usually carries little praise or criticism of its own. This is a mathematical use: it is defined precisely and belongs to working with figures and calculations rather than to ordinary conversation.
“The radius of the circle was exactly five centimeters long.”
- Emotional tone
- Neutral
- Formality
- Specialist/technical
- Intensity
- Not strongly marked
- How common
- Specialized
- Connotation
- Clinical and technical
- Usage feel
- Technical and specialized
Where it naturally appears
- Mathematics
- Geometry
- Academic writing
- Education/classroom
Usage note
In general conversation this sense usually needs explaining — outside its field, people reach for a plainer word.
Natural pattern: radius of …
Word Aura describes common impressions, not a measurement. Tone changes with sentence, speaker, relationship and situation.
More ways to use radius
- “They located it within a radius of 2 miles.”noun
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Common Patterns and Combinations
How this word naturally appears with others.
Word Family
Related forms, grouped by how they connect.
Compound terms
Established multiword terms.
The radius of the circle of curvature.
A line connecting a satellite to the center of the body around which it is rotating.
Related Words
Connected to the same idea, not synonyms.
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Dictionary data from Wiktionary via the Free Dictionary API. Simple meanings, combinations and word intelligence are built from verified reference data, no AI is used to load this page.