What does adelphic mean?

: of or relating to a polygynous marriage in which the wives are sisters or to a polyandrous marriage in which the husbands are brothers.

What is the meaning of Adelphic polyandry?

Fraternal polyandry (from the Latin frater—brother), also called adelphic polyandry (from the Greek ἀδελφός—brother), is a form of polyandry in which a woman is married to two or more men who are brothers. ... The Toda people of southern India practice fraternal polyandry, but monogamy has become prevalent recently.