'Retroactive law' definitions:

Definition of 'Retroactive law'

From: GCIDE

Retroactive \Re`tro*act"ive\, a. [Cf. F. r['e]troactif.] Fitted or designed to retroact; operating by returned action; affecting what is past; retrospective. --Beddoes. [1913 Webster]
Retroactive law or Retroactive statute (Law), one which operates to make criminal or punishable, or in any way expressly to affect, acts done prior to the passing of the law. [1913 Webster]