Sister-in-law

A sister-in-law (plural sisters-in-law) is the sister of one's spouse, the wife of one's sibling, or sometimes the wife of one's spouse's sibling. Relative to a woman, the latter case (typically her husband's brother's wife; that is, the two women have married brothers) is occasionally called a co-sister-in-law, as they are each the sister-in-law of the others husband.

For example, if Jacob and Esau are brothers, Leah being Jacob's wife, and Adah being Esau's wife, then Adah is Jacob's sister-in-law, Leah is Esau's sister-in-law, and Adah and Leah are co-sisters-in-law to one another.

References