Radius vs. Radii — What's the Difference?
By Tayyaba Rehman — Updated on September 17, 2023
"Radius" refers to a straight line from a circle's center to its circumference; "Radii" is its plural form, meaning multiple such lines.
Difference Between Radius and Radii
Table of Contents
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Key Differences
"Radius" is a term derived from Latin, which in geometric contexts, signifies a straight line stemming from the center of a circle (or sphere) extending to its periphery. "Radii," on the other hand, serves as the plural version of "radius," representing more than one such line.
Both "Radius" and "Radii" are instrumental in mathematics, especially geometry, where circles and spheres become subjects of discussion. While "Radius" pertains to one singular line, "Radii" brings forth the idea of multiple such lines or measures within various circles or spheres.
Outside of geometry, "Radius" can embody other meanings, like the extent of a particular area or activity. "Radii," in similar contexts, could denote multiple areas or sectors stemming from a central point, similar to the spokes of a wheel.
In anatomical contexts, the term "Radius" is also employed to describe a bone in the forearm. "Radii" would then refer to these bones in more than one individual or, in rarer cases, instances of duplicated bones.
Regardless of the context, whenever one refers to multiple lines from the center to the circumference of circles (or analogous ideas), "Radii" becomes the correct choice. For a singular context, "Radius" remains apt.
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Comparison Chart
Number
Singular
Plural
Meaning in Geometry
A line from the center to the edge of circle
Multiple such lines in one or more circles
Usage in Anatomy
Refers to a forearm bone
Refers to these bones in multiple individuals
Linguistic Origin
Latin derived term
Plural form of the Latin word "Radius"
Application in Context
Used when referring to one such line
Used when multiple such lines or areas are discussed
Compare with Definitions
Radius
A certain limit or boundary.
The town lies within the radius of the school district.
Radii
Plural form of a straight line from the center of a circle to its circumference.
The circles have varying radii.
Radius
A straight line from a circle's center to its circumference.
The diameter is twice the length of the radius.
Radii
Multiple extents of specific areas or activities.
Different radii were set for the delivery zones.
Radius
The extent of a specific area or activity.
The restaurant delivers within a 10-mile radius.
Radii
Several limits or boundaries.
There are various radii for these delivery services.
Radius
In anatomy, the bone of the forearm on the thumb side.
The x-ray showed a fracture in the radius.
Radii
In anatomy, referring to multiple radius bones.
Both their radii were examined during the anatomy class.
Radius
In classical geometry, a radius of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the Latin radius, meaning ray but also the spoke of a chariot wheel.
Radii
Ranges for multiple broadcasting or reception zones in radio.
The different radio stations have different radii of coverage.
Radius
A line segment that joins the center of a circle with any point on its circumference.
Radii
A plural of radius.
Radius
A line segment that joins the center of a sphere with any point on its surface.
Radius
A line segment that joins the center of a regular polygon with any of its vertices.
Radius
The length of any such line segment.
Radius
A circular area measured by a given radius
Every family within a radius of 25 miles of the city center.
Radius
A bounded range of effective activity or influence
The operating radius of a helicopter.
Radius
A radial part or structure, such as a mechanically pivoted arm or the spoke of a wheel.
Radius
A long, prismatic, slightly curved bone in humans, the shorter and thicker of the two forearm bones, located on the lateral side of the ulna.
Radius
A similar bone in many other vertebrates.
Radius
(anatomy) The long bone in the forearm, on the side of the thumb.
Radius
(zoology) The lighter bone (or fused portion of bone) in the forelimb of an animal.
Radius
(entomology) One of the major veins of the insect wing, between the subcosta and the media; the vein running along the costal edge of the discal cell.
Radius
(geometry) A line segment between any point of a circle or sphere and its center.
Fatima claims to have visited all the bars within a five-mile radius of her Manhattan apartment.
Radius
(geometry) The length of this line segment.
Radius
Anything resembling a radius, such as the spoke of a wheel, the movable arm of a sextant, or one of the radiating lines of a spider's web.
Radius
A right line drawn or extending from the center of a circle to the periphery; the semidiameter of a circle or sphere.
Radius
The preaxial bone of the forearm, or brachium, corresponding to the tibia of the hind limb. See Illust. of Artiodactyla.
Radius
A ray, or outer floret, of the capitulum of such plants as the sunflower and the daisy. See Ray, 2.
Radius
The barbs of a perfect feather.
Radius
The movable limb of a sextant or other angular instrument.
Radius
The length of a line segment between the center and circumference of a circle or sphere
Radius
A straight line from the center to the perimeter of a circle (or from the center to the surface of a sphere)
Radius
A circular region whose area is indicated by the length of its radius;
They located it within a radius of 2 miles
Radius
The outer and slightly shorter of the two bones of the human forearm
Radius
Support consisting of a radial member of a wheel joining the hub to the rim
Radius
In radio, a range for broadcasting or reception.
The radio station has a radius of 50 miles.
Common Curiosities
How is "Radii" used in context?
"Radii" refers to multiple lines from the centers to the circumferences of circles or multiple extents of areas.
In anatomy, what does "Radius" mean?
"Radius" refers to a bone in the forearm on the thumb side.
How do you differentiate between "Radius" and "Radii" in writing?
"Radius" is singular; "Radii" is plural.
Are there other words similar to "Radii" in formation?
Yes, like "cactus" becomes "cacti" and "fungus" becomes "fungi."
Can "Radius" refer to areas beyond geometry?
Yes, "Radius" can denote the extent of an area, activity, or range in various contexts.
What does "Radius" mean in geometry?
"Radius" refers to a straight line from the center of a circle to its circumference.
Can "Radius" and "Radii" be used interchangeably?
No, "Radius" is singular, and "Radii" is plural. Their use depends on the context.
Is "Radii" the singular or plural form?
"Radii" is the plural form of "Radius."
Can "Radii" be used in non-geometric contexts?
Yes, it can denote multiple extents or ranges in various contexts, like broadcasting.
Is "Radii" a Latin term?
"Radii" derives from the Latin word "Radius," meaning "staff" or "rod."
What's the primary thing to remember about "Radius" and "Radii"?
"Radius" is singular and refers to one line or extent, while "Radii" is plural, referring to multiple lines or extents.
How is "Radius" different from "Diameter"?
The diameter is twice the length of the radius, spanning the entire circle.
Is the term "Radius" specific to circles?
In geometry, primarily yes, but "Radius" can also refer to the extent of spheres or activities outside geometry.
Is the term "Radii" used often in daily conversation?
It's more common in academic, scientific, or specific contexts rather than daily conversation.
Can "Radii" refer to the radius bone in anatomy?
Yes, when referring to these bones in multiple individuals or instances.
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Tayyaba RehmanTayyaba Rehman is a distinguished writer, currently serving as a primary contributor to askdifference.com. As a researcher in semantics and etymology, Tayyaba's passion for the complexity of languages and their distinctions has found a perfect home on the platform. Tayyaba delves into the intricacies of language, distinguishing between commonly confused words and phrases, thereby providing clarity for readers worldwide.
