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 资深译员姚坚,毕业于一所培养高级翻译以及跨文化事务专家的精英大学,专注翻译各种与私募资本有关的法律文件。