concubine
/ˈkɒŋkjʊbaɪn/noun
1- chiefly historical (in polygamous societies) a woman who lives with a man but has lower status than his wife or wives〈主史〉（一夫多妻制社会中的）妾, 小老婆, 姨太太。
1.1
- archaic a mistress〈古〉姘妇, 情妇。
派生词
concubinary
/kənˈkjuːbɪnərɪ/ adjective词源
Middle English: from Old French， from Latin concubina, from con- 'with'+cubare 'to lie'.