1. An optical toy consisting of a cylinder with mirrors and colored shapes inside that create shifting symmetrical patterns when the end is rotated.
2. A complex set of events or circumstances.
3. From early 19th century, Greek kalos, "beautiful" + eidos, "form"; + scope, "see".

An optical instrument, consisting of from two to four reflecting surfaces placed in a tube, at one end of which is a small compartment containing pieces of colored glass: on looking through the tube, numerous reflections of these are seen, producing brightly-colored symmetrical figures, which may be constantly altered by rotation of the instrument.