Wiktionary
n. In a polygamous marriage, another wife of a woman's husband.
Usage examples of "co-wife".
Ludmilla was special—Mimi’s granddaughter, daughter in all but fact, and by most special exception and through Mimi’s intervention her co-wife, most junior to most senior.
Not like Gretchen whose first baby is descended both from me (Colonel Ames is my grandson through Lazarus) and from my co-wife Hazel/Gwen (Gretchen is Hazel’s great-granddaughter) - Major Gretchen is a big, strong, strapping Valkyrie, reputed to be sudden death with or without weapons.
My co-wife Gwen/Hazel could steal the spots off a leopard and never disturb his sleep.
Ludmilla was special--Mimi's granddaughter, daughter in all but fact, and by most special exception and through Mimi's intervention her co-wife, most junior to most senior.
Things broke up, the zaftig lady was swept off Miles's hands by two of her co-wives, and he began to make his way across the room back to the Barrayaran ambassador's party.