
1) Radius
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https://www.crosswordclues.com/clue/semidiameter

In geometry, the semidiameter or semi-diameter of a set of points may be one half of its diameter; or, sometimes, one half of its extent along a particular direction. ==Special cases== The semi-diameter of a sphere, circle, or interval is the same thing as its radius — namely, any line segment from the center to its boundary. The semi-diameters ...
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http://en.wikipedia.org/wiki/Semidiameter

• (n.) Half of a diameter; a right line, or the length of a right line, drawn from the center of a circle, a sphere, or other curved figure, to its circumference or periphery; a radius.
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http://thinkexist.com/dictionary/meaning/semidiameter/
Sem`i·di·am'e·ter noun (Math.) Half of a diameter; a right line, or the length of a right line, drawn from the center of a circle, a sphere, or other curved figure, to its circumference or periphery; a radius.
Found on
http://www.encyclo.co.uk/webster/S/63

[
n] - the apparent radius of a celestial body when viewed as a disc from the earth
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http://www.webdictionary.co.uk/definition.php?query=semidiameter
noun the apparent radius of a celestial body when viewed as a disc from the earth
Found on
https://www.encyclo.co.uk/local/20974
No exact match found.