The Collaborative International Dictionary
Leviratical
Levirate \Lev"i*rate\ (l[e^]v"[i^]*r[asl]t), Leviratical \Lev`i*rat"ic*al\ (-r[a^]t"[i^]*kal), a. [L. levir a husband's brother, brother-in-law; akin to Gr. dah`r: cf. F. l['e]virat 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.
The firstborn son of a leviratical marriage was
reckoned and registered as the son of the deceased
brother.
--Alford.
Wiktionary
leviratical
a. Of, relating to, or in accordance with levirate marriage.