v. i. [ Pref. retro- + act. ] To act backward, or in return; to act in opposition; to be retrospective. [ 1913 Webster ]
n. [ Cf. F. rétroaction. ]
a. [ Cf. F. rétroactif. ] Fitted or designed to retroact; operating by returned action; affecting what is past; retrospective. Beddoes. [ 1913 Webster ]
Retroactive law
Retroactive statute
adv. In a retroactive manner. [ 1913 Webster ]