1. An instrument with a point used for drawing circles. It can also refer to a tool with two points for measuring distances on maps or diagrams, or it can be a tool for cutting circles.
For example: Most basic drawing sets contain a pencil, ruler, set square (triangular instrument for drawing angles of ninety degrees), protractor (semicircular instrument to measure angles) and a compass.
2. An instrument with a magnetic revolving needle which points to the North. Used for finding your way and reading maps. Compasses are now obsolete with the discovery of GPS. Compasses have been used for navigation for probably two thousand years. It seems that the compass is a Chinese invention.
For example: If you go walking in the mountains, it is a good idea to take a compass as it will help you find your way.
The introduction of the compass radically changed navigation at sea.
3. (musical) A range of musical notes from a voice or musical instruments.
For example: The high note is well within the compass of the soprano's voice.
This noise is below the compass of the human ear.