- One's husband's brother's wife; or more generally one's spouse's sister-in-law, the sister of one spouse in relation to the siblings of the other spouse.
- (in the plural) The relationship between women who marry brothers
- One's brother-in-law or sister-in-law's sister; that is, one's sibling's spouse's sister (one's sister's husband's sister or one's brother's wife's sister).
- (in the plural) The relationship between women whose brother and sister are married to each other
Generally used in translation, or in countries such as India (Andhra Pradesh) where the local language makes the distinction. In common speech in traditionally English-speaking countries, sister-in-law may be used.
The primary usage is for one's husband's brother's wife.
co- + sister-in-law.