noun
Common
radius
RAY-dee-uhs
Radius (noun) means a straight line from the center of a circle or sphere to its edge, or the length of that line. Example: “Use a compass to draw a circle with a radius of four centimetres.”
noun
1
A straight line from the center of a circle or sphere to its edge, or the length of that line.
"Use a compass to draw a circle with a radius of four centimetres."
"If you double the radius, the circle becomes much larger."
"The radius of the circle is exactly five centimeters."
2
A surrounding area or distance measured from a central point.
"Most of our customers live within a short radius of the shop."
"Residents were asked to stay out of a wide radius around the building."
"Every school within a five-mile radius was closed for the storm."
3
The long bone of the forearm on the thumb side.
"The doctor said the radius in her wrist had healed well."
"The radius runs alongside the ulna in your forearm."
"He fractured his radius after falling off his bike."
How to use radius
Learner’s notesIn plain EnglishThe distance from the center of a circle to its edge, or (loosely) the surrounding area within a given distance; also a bone in the forearm.
Common pairings
within a mile radius
radius of the circle
fractured radius
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Word forms
- Plural
- radii, radiuses
- Third person singular
- radiuses
- Past tense
- radiused
Fill the gap
Can you complete this real example?
Use a compass to draw a circle with a _____ of four centimetres.
Etymology
Borrowed directly from Latin radius, meaning "ray" or "spoke".
Synonyms
View more →Related words
Rhymes for radius
See all rhymes for radius →Frequently asked questions
What does “radius” mean?
The word “radius” means a straight line from the center of a circle or sphere to its edge, or the length of that line. In plain terms, the distance from the center of a circle to its edge, or (loosely) the surrounding area within a given distance; also a bone in the forearm.
How do you pronounce “radius”?
“Radius” is pronounced RAY-dee-uhs (/ˈɹeɪ.di.əs/ in IPA).
How do you use “radius” in a sentence?
Here is “radius” used in a sentence: “The radius of the circle is exactly five centimeters.”
What part of speech is “radius”?
“Radius” is a noun.
Where does the word “radius” come from?
The word “radius” comes from Latin. Borrowed directly from Latin radius, meaning "ray" or "spoke".
Is “radius” a common word?
“Radius” is a fairly common word in modern English.
How many meanings does “radius” have?
“Radius” has 3 distinct senses listed in this dictionary. The most common is: a straight line from the center of a circle or sphere to its edge, or the length of that line.
What is the difference between radius and diameter?
The radius is the straight line from the center of a circle to its edge, while the diameter is a line that passes through the center and connects two opposite points on the edge. The diameter is always exactly twice the length of the radius.
What does radius mean in a phrase like 'within a five-mile radius'?
In this usage, radius refers to a surrounding area or distance measured outward from a central point, such as a location or event. 'Within a five-mile radius' means anywhere inside a circle extending five miles from that point.
Where is the radius bone located in the body?
The radius is the long bone of the forearm on the thumb side, running from the elbow to the wrist. It works alongside the ulna, the other forearm bone, to allow rotation of the hand.
