sundial

n. instrument which indicates the time of day by means of a shadow cast by a vertical shaft onto a flat circular disk

A sundial is a device that measures time by the position of the Sun. The most commonly seen designs, such as the 'ordinary' or standard garden sundial, cast a shadow on a flat surface marked with the hours of the day. As the position of the sun changes, the time indicated by the shadow changes. However, sundials can be designed for any surface where a fixed object casts a predictable shadow.
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Noun
1. timepiece that indicates the daylight hours by the shadow that the gnomon casts on a calibrated dial
(hypernym) timepiece, timekeeper
(part-meronym) gnomon

(n.)
An instrument to show the time of day by means of the shadow of a gnomon, or style, on a plate.
  

sundial
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