Wiktionary
retroactivity
n. 1 The state or characteristic of being retroactive. 2 (context legal English) The application of a law to events that took place before it was made.
Usage examples of "retroactivity".
An order by an Area Rent Director reducing an unapproved rental and requiring the landlord to refund the excess previously collected, was held, with one dissenting vote, not to be the type of retroactivity which is condemned by law.