資料來源 : Webster's Revised Unabridged Dictionary (1913)

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.