sister-wife

noun3

1. •
   In a polygamous marriage, a woman who is simultaneously the sister and co-wife of another.

   • Enmities between sister-wives will [be,] from their having known each other too intimately all their lives, more unmannerly than where they are strangers to each other — 1853
2. •
   A co-wife in general.

   • Yüeh-niang and her sister-wives, all dressed in formal gowns, came out from inside to greet them and ushered them into the rear reception hall — 2006
3. •
   A woman who is simultaneously sister and wife to her spouse.

   • My Grecians shall victorious prove, By me led on to War, the Sister-Wife of Jove. — 1743