wife-in-law

Etymology
From.

Noun

 * 1) A wife in law only, such as one who has abandoned her husband
 * 2) A wife who provides domestic or social support, but not love or affection
 * 3) Another wife of one's husband. Typically used in cases of divorce and subsequent remarriage for one's husband's ex-wife, but sometimes used in polygamy for a co-wife.