弟妇 refers to the wife of one's younger brother.
Topic 1.1: 1.1 Families and Communities in China
弟妇 (dìfù) cheat sheet for homework
儿媳妇 (ér xífù): This term refers to the daughter-in-law, the wife of one's son.
女婿 (nǚxù): This term refers to the son-in-law, the husband of one's daughter.
兄弟姐妹 (xiōng dì jiě mèi): This term refers to siblings, brothers and sisters in a family.