How is your mother-in-law's sister related to you?

Answer 1

Your mother-in-law's sister is your spouse's aunt but is not related to you.

While in Western Culture Spouse's relations are ignored to be anything to you. But in Asian Culture a Mother in Law's Sister will be as Aunt to you as she is to your spouse. It kinda make more sense to me if you see is this way that your brother is considered to brother in law to your spouse, when we say in law we tend to look it only as spousal relation, but actually in law means that after the marriage as per law he/she is your brother or sister in the eyes of law. Thus adultery with in law is not only considered sin but also incestuous.

Answer 2

The English language has no special relationship term for your mother-in-law's sister. She is just "your spouse's aunt."