retroaction

/ˌrɛtroʊˈækʃən/
noun
  1. The act or process of taking effect from a past date; backward action or influence.
    • The retroaction of the new rules meant that some people had to pay extra taxes for last year.
    • Historians study the retroaction of earlier events on later developments.
    • The retroaction of the medication was unexpected, affecting symptoms that had appeared weeks before.
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