ra·di·us 
(rādē-əs)
(rādē-əs)n. pl. ra·di·i (-dē-ī′) or ra·di·us·es
1. Abbr. r or rad. Mathematics
a. A line segment that joins the center of a circle with any point on its circumference.
b. A line segment that joins the center of a sphere with any point on its surface.
c. A line segment that joins the center of a regular polygon with any of its vertices.
d. The length of any such line segment.
2. A circular area measured by a given radius: every family within a radius of 25 miles of the city center.
3. A bounded range of effective activity or influence: the operating radius of a helicopter.
4. A radial part or structure, such as a mechanically pivoted arm or the spoke of a wheel.
5. Anatomy
a. 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.
b. A similar bone in many other vertebrates.
[Latin, ray, spoke of a wheel, radius; see RAY1.]
- unappeasably
- unappetizing
- unappetizingly
- unappreciated
- unappreciative
- unappreciatively
- unapproachability
- unapproachable
- unapproachableness
- unapproachably
- unappropriated
- unapproved
- unapt
- unaptly
- unaptness
- unarguable
- unarguably
- unarm
- unarmed
- unarticulated
- unary operation
- unashamed
- unashamedly
- unasked
- unassailability