concubinage（n.）
14世纪晚期，“做妾的状态； 在没有合法婚姻的情况下共同居住的行为或实践”，源自古法语 concubinage，来自 concubin，源自拉丁语 concubina（见 concubine）。在古罗马法律中，“是指在婚姻没有法律障碍的人之间的永久同居。”
It was distinguished from marriage proper (matrimonium) by the absence of "marital affection"—that is, the intention of founding a family. As no forms were prescribed in the later times either for legal marriage or concubinage, the question whether the parties intended to enter into the former or into the latter relation was often one of fact to be determined from the surrounding circumstances, and especially with reference to a greater or less difference of rank between them. [Century Dictionary]
它与正式婚姻（matrimonium）的区别在于缺乏“婚姻感情”——即建立家庭的意图。由于在后期既没有规定法律婚姻的形式，也没有规定做妾的形式，因此，当事人是否打算进入前者或后者的关系，常常是一个事实问题，需要根据周围的情况，特别是他们之间的地位差异的大小来确定。[世纪词典]
该词起源时间：14世纪末