Co-brother-in-law is a term used to refer to the brother of one's spouse. However, this term may not be widely used and can be confusing to some. Synonyms for this term are widely used to make communication easier. Some of these synonyms include: Brother-in-law (if the spouse has only one brother); Spouse's brother; Brother of my husband/wife; and In-law brother. It is essential to understand the relationships and use the right terminologies in family settings to avoid confusion and misunderstandings. Using appropriate synonyms for co-brother-in-law is one way to ensure clear communication in family conversations.