Definition of "semicircle" [sem•i•cir•cle]

• A half of a circle as divided by a diameter. (noun)
• An object or arrangement of objects or people in the shape of half a circle. (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.

• "According to the theorem, any triangle inscribed in a semicircle is a right triangle, as is shown in the following diagram:"
• "The mind would then only tend to the affirmation of the sole motion of a semicircle, which is not contained in the conception of a semicircle, and does not arise from the conception of any cause capable of producing such motion."
• "The first figure is a semicircle, which is perpendicular to the plane of the circle ABDZ and which starts on the diameter AED and, with point A remaining fixed, rotates to position AKD."