Definition of butterfly effect noun from the Oxford Advanced Learner's Dictionary

 

butterfly effect

 noun
noun
BrE
 
; NAmE
 
 
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the idea that a very small change in one part of a system can have large effects in other parts Word Origin 1980s: from the notion in chaos theory that a butterfly fluttering in Rio de Janeiro could change the weather in Chicago.
See the Oxford Advanced American Dictionary entry: butterfly effect