co-wife
noun [ C ] uk/ˈkəʊˌwaɪf/ /ˈkoʊˌwaɪf/ co-wives
（一夫多妻制下）嫁给同一个男人的女人
one of two or more women who are married to the same man in polygamy (= a system that allows this)
He says his mother's disputes with her co-wife influenced him to choose monogamy. 他说他母亲与他一夫多妻制下的太太发生了矛盾，这影响他最终选择了一夫一妻制。