Definition of: hemisphere

(hem′ə·sfir) noun
1. A half–sphere, formed by a plane passing through the center of the sphere.
2. A half of the terrestrial or of the celestial globe, or a map or projection of the half of either on a plane surface. The world is usually considered as divided either at the equator into the northern and southern hemispheres, or at some meridian between Europe and America into the eastern and western, usually at the twentieth meridian west of Greenwich.
3. Anat. One of two large convoluted, semiovoid masses forming the bulk of the cerebrum. [<F hémisphère <L hemisphaerium <Gk. hēmisphairion <hēmi- half + sphaira a sphere]
—hem·i·spher·ic (hem′ə·sfer′ik) or ·i·cal adjective