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Definition of radius

radius

/ˈreɪ.di.əs/
ra · di · us
Adverb:radially
•
Plural:radii
•
Adjective:radial
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radius Lexical Profile

radius Game Scores & Validity

• noun

1

A straight line extending from the center of a circle or sphere to its circumference or surface, or the length of such a line.

Example

"To calculate the area of the circle, multiply pi by the square of the radius."

2

A circular area of a specified distance surrounding a central point, or the range of an activity or influence.

Example

"The delivery service operates free of charge within a five-mile radius of the store."

3

The thicker and shorter of the two long bones in the human forearm, located on the thumb side and articulating with the wrist and humerus.

Example

"He fractured his distal radius after bracing himself with an outstretched hand during the fall."

Synonyms
View all synonyms for radius

Word Nuance & Usage

The Latin plural 'radii' is standard in mathematics, science, and anatomy, whereas the regular English plural 'radiuses' is acceptable in general everyday usage.

• Rhymes for radius

• Nearby Words

radiothon
radish
radium
radius
radon
raffish
raffle

Word Origin & Etymology

Borrowed in the late 16th century directly from Latin 'radius', meaning 'staff, stake, spoke of a wheel, or ray of light.'

Cite this Entry

Wordmom. (2026). Definition of Radius. In Wordmom Dictionary. Retrieved Nov 5, 2026, from https://wordmom.com/dictionary/radius
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