cha·os cha·os [ká òs] n 1. disorder: a state of complete disorder and confusion 2. or cha·os or Cha·osearliest condition of universe: the unbounded space and formless matter supposed to have existed before the creation of the universe 3. physics apparent disorder: the unpredictability inherent in a system such as the weather, in which apparently random changes occur as a result of the system’s extreme sensitivity to small differences in initial conditions [15th century. Directly or via French from Latin , from Greek khaos “void, abyss,” the original sense in English (source of English gas).]