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
And clinging to the very end of it was the matching end of the lower arm, the radius.
—
Elizabeth Sawchuk, The Conversation, 1 Jan. 2026
Ladis and Jess first met in 2019 after extending their search radius on a dating app.
—Erin Clack, PEOPLE, 31 Dec. 2025
The remarkable discoveries of 2025 went even deeper — into Earth’s innermost layer, which is a hot, solid ball of metal, with a radius of about 759 miles (1,221 kilometers), surrounded by a liquid metal outer core.
—Katie Hunt, CNN Money, 29 Dec. 2025
No evacuation orders have been issued, but LAFD firefighters say that residents living within a one-mile radius of the gas line were asked to shelter in place.
—Dean Fioresi, CBS News, 27 Dec. 2025
See All Example Sentences for radius
Examples are automatically compiled from online sources to
show current usage.
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Elizabeth Sawchuk, The Conversation, 1 Jan. 2026
Ladis and Jess first met in 2019 after extending their search radius on a dating app.
—Erin Clack, PEOPLE, 31 Dec. 2025
The remarkable discoveries of 2025 went even deeper — into Earth’s innermost layer, which is a hot, solid ball of metal, with a radius of about 759 miles (1,221 kilometers), surrounded by a liquid metal outer core.
—Katie Hunt, CNN Money, 29 Dec. 2025
No evacuation orders have been issued, but LAFD firefighters say that residents living within a one-mile radius of the gas line were asked to shelter in place.
—Dean Fioresi, CBS News, 27 Dec. 2025
See All Example Sentences for radius
Cite this Entry
“Radius.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/radius. Accessed 7 Jan. 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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