radius
/ˈreɪdiəs/ (bre, ipa) · /ˈreɪdiəs/ (ame, ipa) · /ˈrā-dē-əs/ (ame, mw)
radius — noun
- radiussingular
- radiiplural
1. in geometry, any line that runs from the centre point of a round shape such as a
in geometry, any line that runs from the centre point of a round shape such as a circle out to its outer boundary is called a radius; the word also names the length of that same line.
Joon drew a circle with a radius of five centimetres on the board.
radius of [measurement] for specifying size
The wheel has a radius of thirty centimetres from hub to rim.
To find the area of a circle, multiply π by the square of its radius.
Heloísa asked the class to calculate the radius from the given diameter.
- diameter
diameter is twice the radius, running from one edge through the centre to the opposite edge
- half-diameter
informal synonym for radius used in some technical contexts
文法句型
the radius of [circle/sphere]
radius of [number + unit]
用法筆記
In geometry, the plural form is radii (ˈreɪ.di.aɪ) rather than radiuses in formal contexts.
常見錯誤
2. the measurement that tells you how far a circular area extends outward from a gi
the measurement that tells you how far a circular area extends outward from a given location; the whole region within that distance is also described using this word.
The blast from the explosion was felt within a two-kilometre radius.
within a [number]-[unit] radius — common phrase for distance from a point
Padma agreed to drive anywhere within a thirty-minute radius of her home.
within a [time]-minute radius — extended use with travel time
All schools within a five-mile radius of the river had to close during the flood.
The app shows restaurants within a small radius of your current location.
- range
range is more general, not necessarily circular; often used for distance a vehicle can travel or a signal can reach
- scope
scope focuses on the limits of what something covers rather than a physical distance around a point
- reach
reach suggests the furthest point you can touch or access, not the whole circular area
文法句型
within a [number]-[unit] radius of [place]
within a radius of [number] [unit]
within [number] [unit] radius
用法筆記
When used with a prepositional phrase, the pattern 'within a [measurement] radius of [place]' is the most common. Native speakers also say 'within [measurement] of [place]' without the word radius, but adding radius makes the circular shape of the area explicit.
常見錯誤
3. a forearm bone that runs from the elbow joint down to the wrist, sitting next to
a forearm bone that runs from the elbow joint down to the wrist, sitting next to the thumb and letting you twist your palm around.
Nikos broke his radius when he tried to catch his fall on the ice.
break one's radius — common injury collocation
The X-ray showed a clean fracture of the radius near the wrist.
fracture of the radius — medical phrasing
The radius sits next to the ulna on the thumb side of the arm.
After the fall, James felt a sharp pain along the radius just above his wrist.
- forearm bone
a general term covering both the radius and the ulna; less precise
- radial bone
formal anatomical term for the radius
- ulna
the other bone in the forearm, located on the little-finger side
文法句型
the radius
fracture of the radius
break one's radius
用法筆記
This anatomical sense is often confused with the ulna, the other forearm bone. The radius is on the thumb side and is slightly shorter but wider; the ulna is on the little-finger side and extends to the elbow tip. In medical writing, the plural is radii or radiuses.