levirate

{ } a. [ L. levir a husband's brother, brother-in-law; akin to Gr. dah`r: cf. F. lévirat leviration. ] Of, pertaining to, or in accordance with, a law of the ancient Israelites and other tribes and races, according to which a woman, whose husband died without issue, was married to the husband's brother. [ 1913 Webster ]

The firstborn son of a leviratical marriage was reckoned and registered as the son of the deceased brother. Alford. [ 1913 Webster ]