What does the word reaction mean?

Usage examples for reaction

  1. Then at last, his work finished, would come inevitable reaction. – A Breath of Prairie and other stories by Will Lillibridge
  2. Sudden and violent was Wemyss's reaction, let loose by the parlourmaid's story. – Vera by Elisabeth von Arnim
  3. And I think of matter and of history in terms of action and reaction. – Children of the Market Place by Edgar Lee Masters