radius - Master This Word
Master this word with our 5-step learning method – Learn English in English
radius Word Meanings
- the distance from the center of a circle to its perimeter
- a straight line from the center to the circumference of a circle
- an area surrounding a certain point
radius Example Sentences
Example sentences are the start of understanding. Don't rush to memorize. First feel how the word works in a sentence.
radius Phonetic & Pronunciation
UK
/ˈreɪdiəs/
US
/ˈreɪdiəs/
radius Word Etymology
radius = ray/spoke + -us, from Latin 'radius' meaning 'ray, spoke'. Visualize a bicycle wheel where the spokes radiate from the hub to the rim, emphasizing distance and connection.
Note 1: These definitions and etymologies are not standard dictionary definitions, but extended explanations provided to help with memorization and understanding of the actual application of words. Through this background information, we strive to make words more vivid and easier to understand, and help you remember their meanings in real life.
Note 2: LexiTalk designs the learning flow around the linguistics principle of “Comprehensible Input.” When learners encounter material that is slightly above their level but still understandable from context, the brain naturally absorbs the language. That’s why we keep every word inside authentic contexts, using examples and associations to help you understand it and use it flexibly.
Read the FAQ explanation of Comprehensible InputReal Context
Radius is the straight-line distance from the center of a circle to its perimeter, and it also designates a line segment of that length. It can describe the radius of a circle in geometry, or a surrounding region defined by a fixed distance from a point, such as a service radius. The word comes from the Latin radius meaning ray or spoke, and visualizing a bicycle wheel with spokes radiating from the hub helps learners picture distance and connection.
Usage Reminders
- Radius is a straight-line distance from center to edge.
- Use the phrase 'the radius of the circle is X' or 'a radius of X' rather than 'the diameter'.
- The plural is radii, not radiuses.
- Radius can also describe a surrounding area or service radius.
- Remember difference between radius and diameter: diameter is twice the radius.
- Common symbol is r for radius in diagrams.
Common Misconceptions
- Radius equals diameter
- Radius is the entire circle or its area
- Radius is always a direction
- Radius always means radius vector
- Radius and diameter are interchangeable in formulas
Thinking Differences
For English speakers, radius is taught as a specific length from center to edge, with a clear contrast to diameter. Learners often mix up the two or think radius is the whole circle.
Learning Tips
- Visualize radius as the spoke distance on a bicycle wheel.
- Remember the symbol r on diagrams.
- Differentiate radius from diameter (diameter = 2 × radius).
- Use radius in non-geometry contexts like service radius.
- Plural is radii; radiuses is incorrect.
- Practice with circles of different sizes to fix the concept.
5-Step Learning Method - Learn English in English
Step 1: Meaning
What does the word 'radius' refer to?
A.A 2-dimensional figure
B.The distance from the center of a circle to any point on its circumference
C.A type of dinosaur
D.A musical instrument
Step 2: Usage
In which of the following sentences is 'radius' used correctly?
A.The radius of the circle is 5 centimeters.
B.She played the radius at the school concert.
C.He drove the car through the radius of the park.
D.The radius and diameter are the same in a circle.
Step 3: Similar Words
Which word is an antonym of 'radius'?
A.Diameter
B.Circumference
C.Perimeter
D.Radial
Step 4: Opposite Words
Where can you see the concept of 'radius' being used in real life?
A.In architecture to design buildings
B.In cooking to measure ingredients
C.In sports to mark the scoring area
D.In medicine to study the human body
Step 5: Mastery
Reflect on when knowing the concept of 'radius' can be useful in daily life.
A.Determining size for clothing
B.Calculating areas for gardening
C.Measuring distances for a road trip
D.Understanding planetary orbits
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