brother in lawbroth·er-in-law
- An example of a brother in law is your sister's husband.
- An example of a brother in law is your husband's brother.
The definition of brother in law is a man who is related to you through marriage to your spouse or sibling, not through blood.
- the brother of one's husband or wife
- the husband of one's sibling
- the husband of a sibling of one's wife or husband
- The brother of one's spouse.
- The husband of one's sibling.
- The husband of the sibling of one's spouse.
- A male relative of one's generation, separated by one degree of marriage:
- (uncommon) Co-brother-in-law: A male relative of one's generation, separated by two degrees of marriage:
(plural brothers in law)
- Alternative form of brother-in-law.