[suhn-dahy-uh
l, -dahyl] 
| an instrument that indicates the time of day by means of the position, on a graduated plate or surface, of the shadow of the gnomon as it is cast by the sun. |
| sun·di·al (sŭn'dī'əl, -dīl') n. An instrument that indicates local apparent solar time by the shadow cast by a central projecting pointer on a surrounding calibrated dial. |
sundial
the earliest type of timekeeping device, which indicates the time of day by the position of the shadow of some object exposed to the Sun's rays. As the day progresses, the Sun moves across the sky, causing the shadow of the object to move and indicating the passage of time. .
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