kaleidoscope

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A tube-shaped optical instrument that is rotated to produce a succession of symmetrical designs by means of mirrors reflecting the constantly changing patterns made by small objects, such as beads or bits of colored glass, at one end of the tube.
• noun A constantly changing set of colors.
• noun A series of changing phases or events.

from The Century Dictionary.

• noun An optical instrument creating and exhibiting, by reflection, a variety of beautiful colors and symmetrical forms.

from the GNU version of the Collaborative International Dictionary of English.

• noun An instrument invented by Sir David Brewster, which contains loose fragments of colored glass, etc., and reflecting surfaces so arranged that changes of position exhibit its contents in an endless variety of beautiful colors and symmetrical forms. It has been much employed in arts of design.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A tube of mirrors containing loose coloured beads etc. that is rotated to produce a succession of symmetrical designs
• noun A constantly changing set of colours, or other things

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a complex pattern of constantly changing colors and shapes
• noun an optical toy in a tube; it produces symmetrical patterns as bits of colored glass are reflected by mirrors