hem ‧ i ‧ sphere /ˈheməsfɪə, ˈhemɪsfɪə $ -fɪr/ BrE AmE noun [countable]
[ Date: 1500-1600 ; Language: Latin ; Origin: hemisphaerium , from Greek , from hemi- 'half' + sphairion 'small sphere' ]
1 . a half of the Earth, especially one of the halves above and below the ↑ equator :
the Northern hemisphere
2 . one of the two halves of your brain
3 . half of a ↑ sphere (=an object which is round like a ball)
—hemispherical /ˌheməˈsferək ə l, ˌhemɪˈsferək ə l/ adjective