levirate

n. custom which required that a man marry his brother's widow if the deceased died childless (Biblical)

Levirate marriage is a type of marriage in which a woman marries one of her husband's brothers after her husband's death, if there were no children, in order to continue the line of the dead husband. The term is a derivative of the Latin word levir, meaning "husband's brother". Levirate marriage has been practiced by societies with a strong clan structure in which exogamous marriage, i.e. that outside the clan, was forbidden. It is or was known in societies including the Punjabis, Jats, Israelites, Huns (Chinese "Xiongnu", "Hsiong-nu", etc.), Mongols, and Tibetans.
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Noun
1. the biblical institution whereby a man must marry the widow of his childless brother in order to maintain the brother's line
(hypernym) institution

adj. leviratical, (Biblical) pertaining to levirate (custom which required that a man marry his brother's widow if the deceased died childless)

(a.)
Alt. of Leviratical