term:

Retroactive

retroactive adj

: extending in scope or effect to a prior time or to conditions that existed or originated in the past
;esp
: made effective as of a date prior to enactment, promulgation, or imposition [a tax] see also ex post facto law
ret·ro·ac·tive·ly adv

ret·ro·ac·tiv·i·ty [-ak-ti-və-tē]
n

Source: Merriam-Webster's Dictionary of Law ©1996. Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Incorporated.