TO LIE WITH CONCUBINES

I always think of the word concubine in historical terms. To me, it brings to mind emperors' harems, but apparently it can also refer to a partner in any sexual relationship where the couple is unmarried. This was the sole definition when the term was borrowed into English in the late thirteenth century from Anglo-Norman, but it has since evolved. That comes from the Latin verb concumbere, which meant "to lie with" and was composed of con-, meaning "with", and cubare, meaning "to lie down". Con-, through Proto-Italic and the earlier Latin word cum, derives from the Proto-Indo-European root kom, which could also mean "next to". Cubare (also the etymon of English cubicle and cubit​) traces to a Proto-Indo-European word sounding like kewb or kub, but definition is uncertain.