Definitions

from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun The apparent radius of a celestial body when viewed as a disk from Earth.

from The Century Dictionary.

  • noun One half the diameter: especially, in astronomy, one half the angular diameter of the sun, moon, or other object showing a disk; the radius.

from the GNU version of the Collaborative International Dictionary of English.

  • 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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun astronomy The apparent radius of a star etc, when viewed from Earth
  • noun archaic, obsolete radius, half of a diameter

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • noun the apparent radius of a celestial body when viewed as a disc from the earth

Etymologies

from Wiktionary, Creative Commons Attribution/Share-Alike License

semi- +‎ diameter

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