Sister - in - law definition: the sister of one's spouse.. See examples of SISTER - IN - LAW used in a sentence. Best Sister in Law Quotes are a beautiful way to express love, gratitude, and the special bond you share with your husband's or wife's sister . sister - in - law (plural sisters - in - law or (colloquial, nonstandard) sister - in - laws ) A female relative of one's generation, separated by one degree of marriage: The sister of one's spouse. Define sister - in - law . sister - in - law synonyms, sister - in - law pronunciation, sister - in - law translation, English dictionary definition of sister - in - law . n. pl. sisters - in - law 1. The sister of one's spouse. 2. The wife of one's sibling. 3. The wife of the sibling of one's spouse. American Heritage® Dictionary...
