Hypertext Webster Gateway: "semidiameter"
From Webster's Revised Unabridged Dictionary (1913) (web1913)
Semidiameter \Sem`i*di*am"e*ter\, n. (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.
From WordNet (r) 1.7 (wn)
semidiameter
n : the apparent radius of a celestial body when viewed as a
disc from the earth
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