plural radii
ˈrā-dē-ˌī 
also radiuses
also radiuses
1
: a line segment extending from the center of a circle or sphere to the circumference or bounding surface
2
a
: the bone on the thumb side of the human forearm
also
: a corresponding part of vertebrates above fishes
b
: the third and usually largest vein of an insect's wing
3
a
: the length of a radius
a truck with a short turning radius
b
: the circular area defined by a stated radius
c
: a bounded or circumscribed area
4
: a radial part
5
: the distance from a center line or point to an axis of rotation
Examples of radius in a Sentence
Measure the radius of the circle.
a radius of 10 inches
The new museum is expected to draw people from a wide radius.
There are three restaurants within a one-block radius of our apartment.
Recent Examples on the Web
The right question for a CISO is not whether the company is patched, but rather what the blast radius looks like when a breach occurs this quarter.
—
Tj Marlin, Forbes.com, 27 May 2026
In-person, 105 countries were represented across NFL OnePass registrants, and 43% of attendees traveled from outside a 50-mile radius.
—Ricky Sayer, CBS News, 26 May 2026
That would make the diameter of the circle two meters as well, giving the circle a radius of one meter and thus an area of π square meters.
—Manon Bischoff, Scientific American, 25 May 2026
One of those features is the radius gap, the curious deficit of planets right between super-Earth and sub-Neptune sizes that the James Webb Space Telescope and Kepler Space Telescope have mapped out.
—Paul Sutter, Space.com, 24 May 2026
See All Example Sentences for radius
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Tj Marlin, Forbes.com, 27 May 2026
In-person, 105 countries were represented across NFL OnePass registrants, and 43% of attendees traveled from outside a 50-mile radius.
—Ricky Sayer, CBS News, 26 May 2026
That would make the diameter of the circle two meters as well, giving the circle a radius of one meter and thus an area of π square meters.
—Manon Bischoff, Scientific American, 25 May 2026
One of those features is the radius gap, the curious deficit of planets right between super-Earth and sub-Neptune sizes that the James Webb Space Telescope and Kepler Space Telescope have mapped out.
—Paul Sutter, Space.com, 24 May 2026
See All Example Sentences for radius
Cite this Entry
“Radius.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/radius. Accessed 28 May. 2026.
Copy CitationKids Definition
radius
noun
ra·di·us
ˈrād-ē-əs
plural radii
-ē-ˌī
also radiuses
also radiuses
1
: the bone on the thumb side of the human forearm
also
: a corresponding bone of other vertebrates
2
: a line extending from the center of a circle or sphere to the circumference or surface
3
a
: the length of a radius
b
: a circular area defined by a given radius
deer may wander within a radius of several miles
4
: a radial part or plane
Etymology
from Latin radius "ray, beam, spoke" — related to radiate, radio, ray entry 2
Medical Definition
radius
noun
ra·di·us
ˈrād-ē-əs
plural radii
-ē-ˌī
also radiuses
also radiuses
: the bone on the thumb side of the human forearm or on the corresponding part of the forelimb of vertebrates above fishes that in humans is movably articulated with the ulna at both ends so as to permit partial rotation about that bone, that bears on its inner aspect somewhat distal to the head a prominence for the insertion of the biceps tendon, and that has the lower end broadened for articulation with the proximal bones of the carpus so that rotation of the radius involves also that of the hand
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