n. The apparent radius of a star etc, when viewed from Earth
n. radius, half of a diameter
the GNU version of the Collaborative International Dictionary of English
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.
The Century Dictionary and Cyclopedia
n. One half the diameter: especially, in astronomy, one half the angular diameter of the sun, moon, or other object showing a disk; the radius.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. the apparent radius of a celestial body when viewed as a disc from the earth
Word Usage
"As the semidiameter was only 28 inches, this large tree could have been but 168 years old."