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.
Hello! I'm Adam Aleksic. This year, I graduated from Harvard University with a degree in Government and Linguistics. There, I co-founded the Harvard Undergraduate Linguistics Society and wrote a thesis on Serbo-Croatian language policy, magna cum laude. In addition to etymology, I also really enjoy philosophy, trivia, vexillology, geography, board games, conlanging, art history, and law.