Brother-in-law

A brother by marriage

A person's brother-in-law is his/her sister's husband, or spouse's brother.

There is some debate over whether the husband of a person's sister-in-law is "brother-in-law" or "brother-in-law by marriage". Most legal definitions indicate such a person is a "brother-in-law". However the term "brother-in-law by marriage" may provide useful clarification.

The plural form is "brothers-in-law".