Webster's Dictionary 
(a.) Alt. of Leviratical
Cyclopedia of Biblical, Theological and Ecclesiastical Literature 
(from the law-Latin term levir, a husband's brother), the name applied to an ancient usage of the Hebrews ( Genesis 38:8 sq.), reordained by Moses ( Deuteronomy 25:5-10; comp. Josephus, Ant. 4:8, 23; Matthew 22:24 sq.), that when an Israelite died without leaving male issue, his brother ( יָבָם , Yabam', which was the specific term applied to this relation), resident with him, was compelled to marry the widow, and continue his deceased brother's family through the first-born son issuing from such union as the heir of the former husband (comp. Jul. Afric. in Eusebius, Hist. Ev. 1:7) . If he was unwilling to do so, he could only be released from the obligation by undergoing a species of insult ( Deuteronomy 25:9). This is illustrated in the case of Ruth (ch. 3, 4), where, however, as an estate was involved. Boaz is styled by a different term ( גֹּאֵל , an Avenger ) . The Talmud contains a very subtile exposition of this statute (see Mishna, Jebamoth, 3:1; comp. Eduj. 4:8, on Deuteronomy 25:9; see also Jebam. 12:6; comp. Selden, Uxor Hebrews 1:12; (Gans, Eherecht, 1:167 sq.). The high-priest appears to have been free from this law ( Leviticus 21:13), and there must doubtless have been other exceptions, especially in the case of aged persons and proselytes (Mishna, Jebam. 11:2). A similar law prevails among the natives of Central Asia (Bernary, p. 34 sq.; Niebuhr, Beschr. p. 70; Bergeron, Voyages, 1:28) and Abyssinia (Bruce, Trav. 2:223), and traces of it existed among the ancient Italians (Diod. Sic. 12:18). This law no doubt originated in the love of offspring, proverbially strong in the Eastern bosom, which sought this method at once of perpetuating a deceased person's name and of procuring progeny for the widow (Jahn's Archeol. § 157). (See Kinsman).
The law, however, was unquestionably attended with great inconveniences, for a man cannot but think it the most unpleasant of all necessities if he must marry a woman whom he has not chosen himself. Thus we find that the brother in some instances had no inclination for any such marriage (Genesis 38; Ruth 4), and stumbled at this, that the first son produced from it could not belong to him. Whether a second son might follow and continue in life was very uncertain; and among a people who so highly prized genealogical immortality of name, it was a great hardship for a man to be obliged to procure it for a person already dead, and to run the risk meanwhile of losing it himself. Nor was this law very much in favor of the morals of the other sex; for, not to speak of Tamar, who, in reference to it, conceived herself justified in having recourse to most improper conduct, it may be observed that what Ruth did ( Ruth 3:6-9), in order to obtain for a husband the person whom she accounted as the nearest kinsman of her deceased husband, is, to say the least; by no means conformable to that modesty and delicacy which we look for in the other sex. A wise and good legislator couldl scarcely have been inclined to patronize any such law but then it is not advisable directly to attack an inveterate point of honor, because. in such a case, for the most part nothing is gained; and in the present instance, as the point of honor placed immortality of name entirely in a man's leaving descendants behind him, it was so favorable to the increase of population that it merited some degree of forbearance and tenderness. Moses therefore left the Israelites still in possession of their established right, but, at the same time, he studied as much as possible to guard against its rigor and evil effects by limiting and moderating its operation in various respects.
In the first place, he expressly prohibited the marriage of a brother's widow if there were children of his own alive. Before this time, brothers were probably in the practice of considering a brother's widow as part of the inheritance, and of appropriating her to themselves, if unable to buy a wife, as the Mongols do, so that this was a very necessary prohibition. For a successor praesumptivus in thoro, whom a wife can regard as her future husband, is rather a dangerous neighbor for her present one's honor, and if she happen to conceive any predilection for the younger brother, her husband, particularly in a southern climate, will hardly be secure from the risk of poison. In the second place, Moses allowed, and, indeed, enjoined the brother to marry the widow of his childless brother; but if he was not disposed to do so, he did not absolutely compel him, but left him an easy means of riddance, for he had only to declare in court that he had no inclination to marry her, and then he was at liberty. This, it is true, subjected him to a punishment, which at first appears sufficiently severe — the slighted widow had a right to revile him in court as much as she pleased; and from his pulling off his shoe and delivering it to the widow, he received the appellation of Baresole, which anybody might apply to him without being liable to a prosecution. But this infliction was, after all, merely nominal, and we find that it did not prevent the rejection of the widow when there was a decided aversion to it on the part of the surviving relative ( Ruth 4:8). The law, however, only extended to a brother living in the same city or country, not to one residing at a greater distance.
Nor did it affect a brother having already a wife of his own. At least, if it had its origin in this, that by reason of the price required for a wife, often only one brother could marry, and the others also wished to do the same, it could only affect such as were unmarried; and in the two instances that occur in Genesis (ch. 38) and Ruth (ch. 4), we find the brother-in-law, whose duty it was to marry, apprehensive of its proving hurtful to himself and his inheritance. which could hardly have been the case if he had previously had another wife, or (but that was at least expensive) could have taken one of his own choice. When there was no brother alive, or when he declined the duty, the levirate law, as we see from the case of Ruth, extended to the nearest relation of the deceased husband, as, for instance, to his paternal uncle or nephew; so that at last even quite remote kinsmen, in default of nearer ones, might be obliged to undertake it. Boaz does not appear to have been very nearly related to Ruth, as he did not so much as know who she was when he met her gleaning in the fields. Nor did she know that he was any relation to her until apprised of it by her mother-in-law. Among the Jews of the present day levirate marriages have entirely ceased, so much so that in the marriage contracts of the very poorest people among them it is generally stipulated that the bridegroom's brother shall abandon all those rights to the bride to which he could lay claim by the law in question (Michaelis, Mos. Recht. 2:197 sq.). See Perizon. De constitutione div. super defuncti fratris uxore ducenda (Hal. 1742); F. Bernary, De Hebraor. leviratu (Berlin, 1835); J. M. Redslob, Die Leviratsche bei den Hebraern (Leipsic, 1836); C. W. F. Walch, De lege levir. ad fratres non germ. sed tribules referenda (G Ö tting. 1763); Htillman, Staatszverf: d. Israel, p. 190 sq.; Rauschenbusch, De lege leviratus (G Ö tting. 1765). (See Marriage).