Gnomon
GNO'MON, noun no'mon. [Gr. an index, to know.]
1. In dialling, the style or pin, which by its shadow shows the hour of the day. It represents the axis of the earth.
2. In astronomy, a style erected perpendicular to the horizon, in order to find the altitude of the sun.
3. The gnomon of a globe, is the index of the hour-circle.