Co-brother is a term popular in several parts of Southern India but is mostly unknown elsewhere. A co-brother is one's wife's sister's husband. Mainstream English has no word to describe such kinship, however the term brother-in-law is frequently used.
This relationship is often referred to as co-brother-in-law, as well.
Sometimes also called as "co brother in law"! Wonder where the term came from originally. My own guess is that it is born of some legalese. Could it be people who are co-opted to be (by marriage) brothers in law?
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