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📕 rednote ID(小红书号)：3881567312

Radius: Definition, Usage & Key Differences Explained (2 meaning)

Meaning 1：center-to-edge distance (radius)

radius 🔊

/ˈreɪdiəs/

The distance from the center of a circle to any point on its edge. It is half the distance across the circle.

Radius diagram showing the distance from a circle's center to its edge.

center-to-edge distance 🔊

➕

/ˈsɛntər tu ɛdʒ ˈdɪstəns/

In geometry, the radius is the straight-line distance from the center of a circle to any point on its circumference, which is exactly half of the circle's diameter.

📁 Category：School Education 🔖 Level：intermediate

📘 Details & Usage

📖 Root Explanation

Latin: radius, meaning 'spoke of a wheel' or 'ray of light'.

💡 Mnemonic

Think of RADIus as RADIal lines that RADIate from a central point, like sun rays.

📖 Example

To draw a perfect circle, first fix the point of your compass, then adjust the radius and rotate it. 🔊 This demonstrates setting the compass to the radius length to draw a circle accurately.

🔗 Collocations

radius of a circle – the distance from the center to the edge of a circle

atomic radius – the distance from the nucleus to the outer electron shell in an atom

curvature radius – the radius of the circle that best fits a curve at a given point

🔄 Synonyms

semidiameter (n.) – half the diameter of a circle; synonymous with radius in geometric contexts

spoke (n.) – a radial line from the center to the rim of a wheel, analogous to a radius

🚫 Antonyms

diameter (n.) – the full distance across a circle through the center, which is twice the radius

🌱 Derivatives

radial (adj.) – relating to or arranged like rays or radii extending from a center

radially (adv.) – in a radial manner; spreading out from a central point

📖 Cultural Story

Derived from Latin 'radius' (spoke, ray), it entered geometry to describe lines radiating from a center, akin to wheel spokes. Now widely used in math, science, and everyday contexts like delivery zones.

Meaning 2：surrounding area (radius)

radius 🔊

/ˈreɪdiəs/

The area or distance around a particular point or place. It describes how far out from a center something extends.

Map illustrating a delivery radius around a central point like a cafe.

surrounding area 🔊

➕

/səˈraʊndɪŋ ˈɛəriə/

In everyday usage, radius refers to the circular area or distance around a specific central point, often used to define limits or ranges for services, events, or influence.

📁 Category：Transportation & Travel 🔖 Level：intermediate

📘 Details & Usage

📖 Example

The new supermarket offers free delivery within a 5-kilometer radius. 🔊 This indicates that free delivery is available for locations up to 5 kilometers from the supermarket.

🔗 Collocations

within a radius – inside the circular area extending from a central point

radius of influence – the extent of impact or control from a central source

blast radius – the area affected by an explosion from its center

🔄 Synonyms

vicinity (n.) – the area near or surrounding a particular place

range (n.) – the extent or area covered by something from a center

periphery (n.) – the outer limits or edge of an area, often circular

🚫 Antonyms

center (n.) – the central point from which a radius extends; the opposite in terms of position