ret·ro·ac·tive 
(rĕt′rō-ăktĭv)
(rĕt′rō-ăktĭv)adj.
Influencing or applying to a period prior to enactment: a retroactive pay increase.
[French rétroactif, from Latin retroāctus, past participle of retroagere, to drive back : retrō-, retro- + agere, to drive; see ag- in the Appendix of Indo-European roots.]
ret′ro·active·ly adv.
ret′ro·ac·tivi·ty n.