hem·i·sphere / ˈheməˌsfi(ə)r/ • n. a half of a sphere. ∎  a half of the earth, usually as divided into northern and southern halves by the equator, or into western and eastern halves by an imaginary line passing through the poles. ∎  a half of the celestial sphere. ∎  (also cerebral hemisphere) each of the two parts of the cerebrum (left and right) in the brain of a vertebrate.DERIVATIVES: hem·i·spher·ic / ˌheməˈsfi(ə)rik; -ˈsferik/ adj.hem·i·spher·i·cal adj.hem·i·spher·i·cal·ly adv.

hemisphere In the form †(h)emisperie, -sphery (XIV) — L. hēmisphærium — Gr. hēmisphaírion (see hēmi- HEMI-, SPHERE); in the form hemisphere (XVI), †-spere (XV) — OF. emisp(h)ere (mod. hémisphère).

hemisphere (hem-iss-feer) n. one of the two halves of the cerebrum, not in fact hemispherical but more nearly quarter-spherical.