sister in lawglossary / SISTER-IN-LAW sister-in-law. The sister of one’s spouse or the wife of one’s brother. • The wife of one’s spouse’s brother is also sometimes considered a sister-in-law. Pl. sisters-in-law. 词条贡献者 译者David,毕业于亚洲顶尖的高级翻译学院,擅长翻译各种与复杂商业诉讼相关的法律文件。