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.

Retroactive law or 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.

Source: Webster's Revised Unabridged Dictionary (1913)