- Sister-in-law is a woman who marries your brother or is your husband's sister.
An example of sister in law is the sister of your brother.
- the sister of one's husband or wife
- the wife of one's brother
- the wife of the brother of one's husband or wife
nounpl. sisters-in-law sisters-in-law
- The sister of one's spouse.
- The wife of one's sibling.
- The wife of the sibling of one's spouse.
The plural sister-in-laws is occasionally seen, but this is considered incorrect by most sources; see, for example, , despite being a common construction in American English.