ret‧ro‧spec‧tive1 [usually before noun]
related to or thinking about the past:
a retrospective study of 110 patients
2SCLPG British English
a law or decision that is retrospective is effective from a particular date in the past [= retroactive]:
Teachers settled for a 4.2% pay rise with retrospective effect from 1 April.
The new rule will be applied retrospectively.