Webster's Dictionary 
(1): (n.) Any place of retreat and security.
(2): (n.) An institution for the protection or relief of some class of destitute, unfortunate, or afflicted persons; as, an asylum for the aged, for the blind, or for the insane; a lunatic asylum; an orphan asylum.
(3): (n.) A sanctuary or place of refuge and protection, where criminals and debtors found shelter, and from which they could not be forcibly taken without sacrilege.
Hastings' Dictionary of the Bible 
Holman Bible Dictionary 
Cyclopedia of Biblical, Theological and Ecclesiastical Literature 
( מַקְלָט , Miklat', Φυγαδεῖον , "Refuge"), a place of safety, where it is not permitted to offer violence to, or touch any person, even though a criminal.
I. Such a purpose was served (see Mishna, Maccoth, 2, 1-3; comp. Philo, De Profugiis, in his Opp. 1, 546 sq.) for the unpremeditated murderer, in accordance with an ancient usage, by the altar (in the Tabernacle and Temple, Exodus 21:14; 1 Kings 1:50), the horns of which were seized by the refugee. (See Altar). Under the Law there were instituted, in order to rescue such manslayers from the (doubtless very barbarous) blood-revenge ( Numbers 35:6 sq.; Deuteronomy 4:41 sq.; Deuteronomy 19:3 sq.; comp. Exodus 21:13; Josephus, Ant. 4, 7, 4), six Free Cities ( עָרִי מַקְלָט , Sept. Πόλεις Φυγαδευτηρίων , Πόλεις Καταφυγῆς , Vulg. Urbes Fugitivorum, Auth. Vers. "cities of refuge"), which lay in different parts of the entire country, and were some of them sacerdotal, others Levitical cities, namely, east of the Jordan, Bezer, Ramoth-Gilead, and Golan; west of the Jordan, Kedesh, Shechem, and (Hebron) Kirjath-Arba ( Joshua 20:7-8). Here the fugitive, after having undergone a strict investigation to prove that he had not committed the slaughter intentionally, was obliged to remain until the death of the then incumbent of the high-priesthood (comp. the similar exile according to the Athenian statutes, Heffter, Athen. Gerichtsverf. p. 136); if he quitted the city earlier, the blood-avenger might kill him with impunity ( Numbers 35:24 sq.). The roads to the cities of refuge were to be kept in good order ( Deuteronomy 19:3; for other particulars, see Maccoth, 2, 5; Otho, Lex. Rabb. p. 66; on the boundaries of these cities, see the Mishna, Maaser.3, 10). Willful murderers ( Numbers 35:12; compo Mishna, Miaccoth, 2, 6) were to be put to death, after a legal investigation, even if they had escaped to a city of refuge. See generally Michaelis, Mos. Recht, 2, 434 sq.; Moebii Disputat. Theol. p. 105 sq.; Wichmannshausen, De Praesidiariis Levitarum Urbibus (Viteb. 1715); Reis, De Urbibus Refugii V. T. Eorumque Fructu (Marburg, 1753); Osiander, De asylis Hebr. (Tubing. 1672, also in Ugolini Thesaur. 31). The reason for assigning the Levitical cities for this purpose was probably in part from their connection with the sacredness of Jehovah, and partly because the Levites, as guardians of the Law, were present to decide concerning the murder as to whether it was intentional or not (see Carpzov, Appar. p. 340). It is not easy to explain the connection of the expiration of the bloods revenge with the death of the high-priest, except that this was regarded as beginning a fresh era (Tabulme noave). Baihr (Symbol. 2, 52), following Maimonides (More Nevochim), advances the not imlprobable supposition that the high-priest was so eminently the head of the theocracy, and representative of the whol nation, that upon his demise every other death should be forgotten, or, at least, mortal enmities buried (for allegorical significations, see Philo, De profugiis, 1, 466). (See Blood-Revenge).
II. Grecian and Roman antiquity likewise affords mention of the light of asylum (Serv. Ad Aen. 8, 341), not only at altars, and temples, and sacred places (Herod. 2, 113; Eurip. Hec. 149; Pausan. 2, 5, 6; 3, 5, 6; Dio Cass. 47, 14; Strabo, 5, 230; Tacit. Annal.3, 60, 1; Flor. 2, 12), but also in cities and their vicinity (Polyb. 6, 14, 8; comp. Potter, Greek Ant. 1, 48; see Cramer, De ara exter. templi sec. p. 16 sq.; Dougtaei Anal. 1, 102 sq.), for insolvent debtors (Plutarch. De vitando aere al. 3), for slaves who had fled from the severity of their masters (comp. Philo, Opp. 2, 468), also for murderers. An especially famous city of exemption was Daphne, near Antioch ( 2 Maccabees 4:33), as also the temple of Diana at Ephesus (Strabo, 14:641; Apollon. Ephes. Ep. 65). But as the abuse of the privileges of asylum often interfered with criminal jurisprudence, it was circumscribed by Tiberius throughout the Roman empire (Suet. Tib. 37; comp. Ernesti Excurs. in loc.). On the immunities referred to in Acts 16:12, (See Colony). (On cities of refuge in Abyssinia, see Ruppell, 2:71.)
(See City Of Refuge).
III. The privilege of asylum was retained in the Christian Church, probably in imitation of the cities of refuge, under the old dispensation. All criminals who fled to such asylums were held to be safe, and any person violating an asylum was punished with excommunication. All Christian churches, in the early ages, possessed this privilege of affording protection or asylum. It was introduced by Constantine, and first regulated by law under the emperors Theodosius the Great, Arcadius, Honorius, Theodosius, and Justinian. The multiplication of these privileged places soon became exceedingly inconvenient, and it was found necessary, from time to time, to circumscribe the ecclesiastical right of asylum by various limitations. Bishops and councils became jealous of the interference of the civil power in this matter: they contended strongly for the right of sanctuary, and continued to uphold it to an injurious and demoralizing extent. The privilege was extended by the councils of Orange, A.D. 441; of Orleans, 511; of Arles, 541; of Macon, 586; of Rheims, 630; of Toledo, 681. It was recognised:and confirmed by Charlemagne and his successors. The practice long prevailed in popish countries; but the evils at length became so enormous, that even popes and councils were obliged to set limits to the privilege. The custom has now become extinct, or has been greatly reformed. — Bingham, Orig. Eccles. bk. 8, ch. 11.
IV. The laws of King Alfred recognized the right of asylum in England. It was not till the year 1487, in the reign of Henry VII, that by a bull of Pope Innocent VIII it was declared that, if thieves, robbers, and murderers, having taken refuge in sanctuaries, should sally out and commit fresh offenses, and then return to their place of shelter, they might be taken out by the king's officers. It was only by an act of Parliament, passed in 1534, after the Reformation, that parsons accused of treason were debarred of the privilege of sanctuary. After the complete establishment of the Reformation, however, in the reign of Elizabeth, neither the churches nor sanctuaries of any other description were allowed to become places of refuge for either murderers or other criminals. But various buildings and precincts in and near London continued for a long time after this to afford shelter to debtors. At length, in 1697, all such sanctuaries, or pretended sanctuaries, were finally suppressed by the Acts 8, 9 William III, chap. 26. — Penny Cyclop. s.v.
On the subject generally, see Helfrecht, Abhandluny von den Asylen (Haf. 1801, 8vo); Dann, Ueber den Ursprung des Asylrechts und dessen Schicksale und Ueberreste in Europa (in Reyscher and Wilda, Zeitschrift fur deutsches Recht,3, 327 sq.); Pauly, leall-Enlcykl. 1, 889 sq.; comp. Lielbner, De asylis (Lips. 1673); Moebius, Ασυλολογία (Lips. 1673); Kampm Ü ller, De Asyllspontificorum (Lips. 1711); Bdhner, De Sanctitate Ecclesiar. (Hal. 1732); Zech, De Jure Casyli Eccl. (Ingolst. 1761; also in Schmidt's Thes. Jur. Eccl. 5, 284); Neininger, De Orig. Asyli Eccl. (Frib. 1788). Other treatises are by Benzel (in his Dissertt. Acad. 1, 437), Carlholm (Upsal. 1682), Goetze (Jen. 1660), Ehrenbach (Tub. 1686), Engelbrecht (Helmst. 1720), Gronwall (Lips. 1726), Ginther (Lips. 1689), Lobbetius (Leod. 1641), Tophoff (Paderb. 1839), Lyncker (Freft. 1698). See Sanctuary
International Standard Bible Encyclopedia 
a - sı̄´lum : The custom of fleeing to specially sacred places to obtain the protection of a deity is found all over the world (Post, Grundriss , II, 252ff). In ancient Israel we meet with it in two forms - the asylum of the altar and the asylum of the cities of refuge. The altar at the House of God was a place to which persons in danger fled for protection ( 1 Kings 1:50; 1 Kings 2:28 ). It had horns and must not be confused with the altars of earth or stone that were used for lay sacrifices. See Altar; Sanctuary . Exodus 21:14 provides that a murderer is to be taken from the altar to be put to death. The law of the cities of refuge proceeds upon a somewhat different principle. Its objects are (1) to shield a homicide from the avenger of blood until trial, and (2) to provide a refuge for the manslayer who has not been guilty of murder. There is one reference to the institution in the history of the kingdom ( 2 Samuel 14:14 ). For the legal and geographical information, see Cities Of Refuge; Homicide .