lev·i·rate 
(lĕvər-ĭt, -ə-rāt′, lēvər-ĭt, -və-rāt′)
(lĕvər-ĭt, -ə-rāt′, lēvər-ĭt, -və-rāt′)n.
The practice of marrying the widow of one's childless brother to maintain his line, as required by ancient Hebrew law.
[From Latin lēvir, husband's brother; see daiwer- in the Appendix of Indo-European roots.]
lev′i·ratic (-rătĭk), lev′i·rati·cal adj.