. [ L. retro, adv., backward, back. Cf. Re-. ] A prefix or combining form signifying backward, back; as, retroact, to act backward; retrospect, a looking back. [ 1913 Webster ]

v. i. [ Pref. retro- + act. ] To act backward, or in return; to act in opposition; to be retrospective. [ 1913 Webster ]

n. [ Cf. F. rétroaction. ] 1. Action returned, or action backward. [ 1913 Webster ]

2. Operation on something past or preceding. [ 1913 Webster ]

a. [ Cf. F. rétroactif. ] 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 ]

adv. In a retroactive manner. [ 1913 Webster ]

v. t. [ Pref. retro- + cede: cf. F. rétrocéder. ] To cede or grant back; as, to retrocede a territory to a former proprietor. [ 1913 Webster ]

v. i. [ L. retrocedere; retro backward, back + cedere to go. See Cede. ] To go back. [ 1913 Webster ]

a. [ L. retrocedens, p. pr. ] Disposed or likely to retrocede; -- said of diseases which go from one part of the body to another, as the gout. [ 1913 Webster ]

n. [ Cf. F. rétrocession. See Retrocede. ] 1. The act of retroceding. [ 1913 Webster ]

2. The state of being retroceded, or granted back. [ 1913 Webster ]

3. (Med.) Metastasis of an eruption or a tumor from the surface to the interior of the body. [ 1913 Webster ]

n. [ Pref. retro- + choir. ] (Eccl. Arch.) Any extension of a church behind the high altar, as a chapel; also, in an apsidal church, all the space beyond the line of the back or eastern face of the altar. [ 1913 Webster ]