[L. dies, a day.] An instrument constructed to show the hour of the day from the position of the shadow of a style cast by the sun on the face of a dial-plate. It consists of a straight rod or style attached to a plane surface, which is graduated in such a way that the shadow points to the correct time of day as shown by the sun. The style is placed in a direction parallel to the earth's axis. The time shown by a sun-dial is true solar time.