hemisphere

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

• noun A half of a sphere bounded by a great circle.
• noun A half of a symmetrical, approximately spherical object as divided by a plane of symmetry.
• noun Either half of the celestial sphere as divided by the ecliptic, the celestial equator, or the horizon.
• noun Either the northern or southern half of the earth as divided by the equator or the eastern or western half as divided by a meridian.
• noun Either of the lateral halves of the cerebrum; a cerebral hemisphere.
• noun Either of the lateral halves of the cerebellum; a cerebellar hemisphere.

from The Century Dictionary.

• noun A half-sphere; one half of a sphere or globe formed by a plane passing through the center. Specifically
• noun Half of the terrestrial globe; also, half of the celestial globe, or of the surface of the heavens.
• noun A map or projection of half of the terrestrial or the celestial sphere.
• noun In anatomy, either of the two large convex and convoluted masses, one on each side, which together with the fornix, corpus callosum, thalamencephalon, mesencephalon, and olfactory lobes make up the cerebrum. See brain, cerebrum, and cerebral.

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

• noun A half sphere; one half of a sphere or globe, when divided by a plane passing through its center.
• noun Half of the terrestrial globe, or a projection of the same in a map or picture.
• noun The people who inhabit a hemisphere.
• noun (Anat.) See Brain.
• noun (Physics) two hemispherical cups forming, when placed together, a cavity from which the air can be withdrawn by an air pump; -- used to illustrate the pressure of the air. So called because invented by Otto von Guericke at Magdeburg.

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

• noun either half of the cerebrum
• noun half of the terrestrial globe
• noun half of a sphere