in Astronomy, the withdrawing of a star or planet, or its sinking below the horizon. Astronomers and poets make three different kinds of setting of the stars, viz. the cosmical, acronycal, and heliacal.

in nautical language. To set the land or the sun by the compass, is to observe how the land bears on any point of the compass, or on what point of the compass the sun is; also, when two ships sail in sight of each other, to mark on what point the chased bears, is termed setting the chase by the compass.