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# radius

noun (a radius, radii or radiuses)

«radius» in the English dictionary: everyday — its meanings, how the lessons use it, and examples, each with its tree on Mova.

## Everyday

1. (maths) A straight line from the centre of a circle to its edge, or the length of that line. [tree →](https://mova.elamur.ai/free/en/corpora/dictionaries/school/R/radius/#m1)
2. A distance around a place in every direction: «within a 5-mile radius». [tree →](https://mova.elamur.ai/free/en/corpora/dictionaries/school/R/radius/#m2)
3. (body) One of the two bones in the forearm, on the thumb side. [tree →](https://mova.elamur.ai/free/en/corpora/dictionaries/school/R/radius/#m3)

### In the lessons

In maths the radius is half the diameter: diameter = 2 × radius. The area of a circle is π × r × r and the circumference is 2 × π × r. In everyday life «within a radius of» means within that distance all around. Phrases: «within a radius of», «radius and diameter».

### Examples

- The radius of this circle is 4 cm, so the diameter is 8 cm. [tree →](https://mova.elamur.ai/free/en/corpora/dictionaries/school/R/radius/#x1)
- Draw a circle with a radius of 3 cm using a compass. [tree →](https://mova.elamur.ai/free/en/corpora/dictionaries/school/R/radius/#x2)
- All pupils living within a two-mile radius can walk to school. [tree →](https://mova.elamur.ai/free/en/corpora/dictionaries/school/R/radius/#x3)
- He broke his radius when he fell off the trampoline. [tree →](https://mova.elamur.ai/free/en/corpora/dictionaries/school/R/radius/#x4)
- The radius goes from the centre to the edge. [tree →](https://mova.elamur.ai/free/en/corpora/dictionaries/school/R/radius/#x5)
- A circle's area is π times the radius squared. [tree →](https://mova.elamur.ai/free/en/corpora/dictionaries/school/R/radius/#x6)

### Note

Plural: radii (RAY-dee-eye) in maths, radiuses also accepted. Maths: radius = diameter ÷ 2; diameter = radius × 2.

## On Mova

- [Trees and pragmatics of «radius» in the school dictionary](https://mova.elamur.ai/free/en/corpora/dictionaries/school/R/radius/): every meaning and example parsed by Mova, with its dependency tree and frames.
- [«radius» in the school dictionary](https://mova.elamur.ai/free/en/dictionaries/school/w/radius.html) on Mova free.