1 half of a sphere.
2 a half of the earth, esp. as divided by the equator (into northern and southern hemisphere) or by a line passing through the poles (into eastern and western hemisphere).
Derivatives:
hemispheric adj. hemispherical adj.
Etymology: OF emisphere & L hemisphaerium f. Gk hemisphaira (as HEMI, SPHERE)
Useful english dictionary. 2012.