hemicyclium

[ hem-i-sik-lee-uh m ]
/ ˌhɛm ɪˈsɪk li əm /

noun

a sundial in the form of a concave quarter sphere having a rodlike gnomon lying within one radius and marked on its surface with arcs that lie in the same plane as the gnomon.
Also hemicycle.

Origin of hemicyclium

From Latin; see origin at hemicycle