con·cu·bine 
(kŏngkyə-bīn′, kŏn-)
(kŏngkyə-bīn′, kŏn-)n.
1. Law A woman who cohabits with a man without being legally married to him.
2. In certain societies, such as imperial China, a woman contracted to a man as a secondary wife, often having few legal rights and low social status.
[Middle English, from Old French, from Latin concubīna : com-, com- + cubāre, to lie down.]