radius
B2Neutral to formal, primarily technical/scientific.
Definition
Meaning
A straight line from the center to the circumference of a circle or sphere; a measure of distance from a central point.
The length of such a line; a specified distance or area from a central point; the thicker of the two long bones in the human forearm; a radial or radiating part.
Linguistics
Semantic Notes
Primarily a technical term in geometry and anatomy; its 'distance from a point' meaning is common in everyday contexts (e.g., 'within a 5-mile radius'). It has an irregular plural: radii (standard) or radiuses (less common, often for non-technical senses).
Dialectal Variation
British vs American Usage
Differences
No significant differences in meaning. British English may slightly favor 'radii' for all plurals; American English may accept 'radiuses' more readily in non-scientific contexts.
Connotations
Identical. Conveys precision, measurement, and centrality.
Frequency
Equally common in both varieties in technical contexts. Slightly less common in everyday UK speech compared to US, where 'radius' is frequently used in news, real estate, and business (e.g., 'delivery radius').
Vocabulary
Collocations
Grammar
Valency Patterns
within a [measurement] radius of [place]a radius of [measurement] from [point]the [adjective] radiusVocabulary
Synonyms
Strong
Neutral
Weak
Vocabulary
Antonyms
Phrases
Idioms & Phrases
- “Within striking radius (close enough to attack)”
- “Outside the radius of (beyond the scope/influence of)”
Usage
Context Usage
Business
Used to define service areas, e.g., 'Our delivery radius is 10 miles from the store.'
Academic
Central to geometry, physics, astronomy, and anatomy. Precise measurement.
Everyday
Describing how far something is from a location, e.g., 'We looked for cafes within a short radius of the hotel.'
Technical
Exact measurement in engineering, mathematics (e.g., 'the radius of curvature'), medicine (forearm bone).
Examples
By Part of Speech
verb
British English
- (Rare as verb) The path will radius around the old oak tree.
American English
- (Rare as verb) The new highway will radius the northern edge of the city.
adverb
British English
- (Not standard)
American English
- (Not standard)
adjective
British English
- The radius bone was fractured.
- They measured the radius dimension.
American English
- He has a radius fracture.
- Check the radius measurement on the blueprint.
Examples
By CEFR Level
- Draw a circle with a radius of 3 centimetres.
- The school is within a one-mile radius.
- The explosion damaged buildings within a half-kilometre radius.
- The radius of the Earth is about 6,371 kilometres.
- The search party covered a 10-mile radius from the last known position.
- The curvature radius of the lens must be calculated precisely.
- The policy's impact had a surprisingly wide social radius, affecting communities far beyond the target area.
- A comparative analysis of the ionic radii revealed patterns in the periodic table.
Learning
Memory Aids
Mnemonic
Imagine a RADIO with its signal spreading out in a circle. The RADIUS is how far that signal reaches from the central radio tower.
Conceptual Metaphor
INFLUENCE/IMPACT IS A CIRCLE (e.g., 'the blast radius of the scandal'). CONTROL/REACH IS A CIRCULAR AREA (e.g., 'within the radius of her authority').
Watch out
Common Pitfalls
Translation Traps (for Russian speakers)
- Не переводить как 'радиус' в анатомическом контексте без уточнения. В анатомии 'radius' — это 'лучевая кость'.
- Внимание на множественное число: 'radii' (радиусы) /'reɪ.di.aɪ/.
Common Mistakes
- Using 'diameter' when 'radius' is meant (and vice versa).
- Incorrect plural: 'radius' -> 'radiuses' is acceptable but 'radii' is preferred, especially in writing.
- Misspelling as 'radious'.
Practice
Quiz
In human anatomy, the 'radius' is:
FAQ
Frequently Asked Questions
The standard plural is 'radii' (/ˈreɪ.di.aɪ/). The form 'radiuses' is also acceptable, especially in non-technical contexts when referring to distances (e.g., 'several search radiuses').
The radius is the distance from the centre of a circle to its edge. The diameter is the distance across the circle through the centre, which is exactly twice the length of the radius.
It is very rare and highly technical (e.g., in machining or describing a curved path). In 99% of cases, 'radius' is used only as a noun.
It is neutral but precise. It is formal in geometry and science. In everyday use (e.g., 'within walking radius'), it is standard and not overly formal.