AskDefine | Define radius

Dictionary Definition



1 the length of a line segment between the center and circumference of a circle or sphere [syn: r]
2 a straight line from the center to the perimeter of a circle (or from the center to the surface of a sphere)
3 a circular region whose area is indicated by the length of its radius; "they located it within a radius of 2 miles"
4 the outer and slightly shorter of the two bones of the human forearm
5 support consisting of a radial member of a wheel joining the hub to the rim [syn: spoke] [also: radii (pl)]

User Contributed Dictionary

see Radius



radius, ‘ray’.



  1. The long bone in the forearm, on the side of the thumb.
  2. A line segment between any point on the circumference of a circle and its center/centre.
  3. The length of this line segment.

Related terms


line segment
length of this line segment

Crimean Tatar




radius (line segment or length of this line segment).





radius (conditional mood of radii)
  1. would radiate



radius (plural: radii)
  1. ray (of light)
  2. staff, rod
  3. spoke (of a wheel)

Extensive Definition


In classical geometry, a radius (plural: radii) of a circle or sphere is any line segment from its center to its perimeter. By extension, the radius of a circle or sphere is the length of any such segment. The radius is half the diameter. In science and engineering the term radius of curvature is commonly used as a synonym for radius.
More generally—in geometry, engineering, graph theory, and many other contexts—the radius of something (e.g., a cylinder, a polygon, a graph, or a mechanical part) is the distance from its center or axis of symmetry to its outermost points. In this case, the radius may be more than half the diameter.
The relationship between the radius and the circumference of a circle is r=\frac.
To compute the radius of a circle going through three points P_1, P_2, P_3, the following formula can be used:
where \theta is the angle \angle P_1 P_2 P_3.
A radius may also be applied to arithmetic. Where 4,5,6,7,8,9 and 10 can be in a three number radius of 7.


Regular polygons are sometimes said to have a radius, defined as the distance from the center to a vertex. This is the same as the radius of a circumscribed circle with the same center. This latter formulation is sometimes used to define the radius of an arbitrary polygon and is called the circumradius.
radius in Arabic: شعاع
radius in Asturian: Radiu (xeometría)
radius in Min Nan: Poàⁿ-kèng
radius in Bosnian: Poluprečnik
radius in Bulgarian: Радиус
radius in Catalan: Radi (geometria)
radius in Chuvash: Радиус
radius in Czech: Poloměr
radius in Danish: Radius (cirkel)
radius in German: Radius
radius in Modern Greek (1453-): Ακτίνα (γεωμετρία)
radius in Spanish: Radio (geometría)
radius in Esperanto: Radiuso
radius in Basque: Erradio (geometria)
radius in French: Rayon (géométrie)
radius in Galician: Raio (xeometría)
radius in Korean: 반지름
radius in Indonesian: Radius
radius in Icelandic: Geisli (rúmfræði)
radius in Italian: Raggio (geometria)
radius in Hebrew: רדיוס
radius in Swahili (macrolanguage): Nusukipenyo
radius in Latvian: Rādiuss
radius in Luxembourgish: Radius
radius in Lithuanian: Spindulys
radius in Macedonian: Радиус
radius in Dutch: Straal (wiskunde)
radius in Japanese: 半径
radius in Norwegian: Radius
radius in Norwegian Nynorsk: Radius
radius in Polish: Promień
radius in Portuguese: Raio
radius in Romanian: Rază
radius in Quechua: Illwa
radius in Russian: Радиус
radius in Simple English: Radius
radius in Slovak: Polomer (kružnica)
radius in Slovenian: Polmer
radius in Serbian: Полупречник
radius in Finnish: Säde
radius in Swedish: Radie
radius in Tamil: ஆரம்
radius in Thai: รัศมี
radius in Vietnamese: Bán kính
radius in Turkish: Yarıçap
radius in Ukrainian: Радіус
radius in Chinese: 半径

Synonyms, Antonyms and Related Words

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