Lat. In the civil- law. A doctrine or fiction of the law by which the restoration of a person to any status or right formerly possessed by him was considered as relating back to the time of his original loss or deprivation; particularly in the case of one who, having been taken prisoner in war, and having escaped and returned to Home, was regarded, by the aid of this fiction, as having never been abroad, and was thereby reinstated in all his rights. Inst. 1, 12, 5. The term is also applied, in international law, to the recapture of property taken by an enemy, and its consequent restoration to its original owner. Postliminium fingit eum qui captus est in civitate semper fuisse. Postliminy feigns that he who has been captured has never left the state. Inst. 1, 12, 5; Dig. 4’J, 51

Another definition:

(Lat. from post, after, and limen, a threshold). In the Civil Law. The return or restoration of a person to a former estate or right; sometimes, in English, “postliminy.” A fiction applied in the case of a person who had been taken prisoner by an enemy, and afterwards returned from captivity, by which he was supposed never to have been abroad, and was on this ground restored to his former rights. Postliminium fingit eum qui captus est in civitate semper fuisse, postliminy supposes that he who was taken prisoner had always been in the state. Inst. 1. 12. 5. See Dig. 49. 15. Postlim,inium included things as well as persons. Paulus, in the Digests, defines it to be jus amissae rei redpiendae ab extraneo, et in statum, pristinum restituendae, inter nos ac liberos populos regesque moribus, legibus constitutum. Nam quod bello amisimus, aut etiam citra bellum, hoe si rursus .redpia/mus dicimur postliminio recipere, the right of receiving a lost thing from a foreigner, and of restoring it to its former state, established between us and free nations and kings, by customs and by laws. For whatever we have lost in war, or even not in war, if we receive it again, we are said to receive it postliminio. Dig. 49. 15. 19, pr. Postliminium is thus analyzed and explained in the Institutes : It is called postliminium from limjen (threshold), and post (after) . ‘ Wherefore we properly say of one who was taken by an enemy, and afterwards came into our borders or limits, that he has returned postliminio. For as the threshold of a house makes, as it were, the limit or boundary of it, so the ancients chose to call the boundary or border of the empire its threshold. Hence limen (a threshold) came to be used in the sense of a limit (finis), and boundary (terminus). And hence the word postliminium, was framed, and used to signify that a person had returned to the same threshold which he had lost; ab eo postliminium, dictum, est, quia ad idem limen revertebatur quod amiserat. So that now a prisoner who is recovered from an enemy, and returns home, is supposed to have returned in postliminy, that is, in the way explained. Inst. 1. 12. 5. In the Law of Nations. A right whicli arises from a return mi limen, that is, to the borders of one’s country. Grotius de Jur. Belli, lib. 3, c. 9, § 2. A term derived from the Roman law, and extensively used in public law. See its etymology explained by Grotius de Jure Belli lib. 3, c. 9, § 1. See his whole chapter, “De Postliminio.” The term is used in maritime law. See Locc. de Jur. Mar. lib. 2, c. 4.