Definition of "semidiameter" []

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

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "As the semidiameter was only 28 inches, this large tree could have been but 168 years old."
• "Each of the laminae can be seen to be composed of two, three, or four layers of ligneous tubes; but supposing each ring the growth of one year, and the semidiameter of a mowana of one hundred feet in circumference about seventeen feet, if the central point were in the centre of the tree, then its age would lack some centuries of being as old as the"
• "On the same day, at Des Moines, Newcomb could perceive, through somewhat hazy air, no long rays, and the four-pointed outline of the corona reached at its farthest only a _single semidiameter_ of the moon from the limb."