/
ˈkeɪɒs/
n.
  - complete disorder and confusion. ▸Physics  the property of a complex system whose behaviour is so unpredictable as to appear random, owing to great sensitivity to small changes in conditions. 
- the formless matter supposed to have existed before the creation of the universe.
Etymology
C15 (denoting a gaping void): via Fr. and L. from Gk khaos ‘vast chasm, void’.