When the word concierge was first used in English in 1646, it referred to caretakers of large estates. Later on it could also mean "janitor", "porter", and "warden", and eventually came to be applied to those people who work in hotels. The term most likely comes from the Old French word cumcerges, which described an official tasked with maintaining royal palaces. Cumcerges is thought to trace to Vulgar Latin conservius and Latin conservus, which meant "fellow slave". Infuriatingly, none of the sources I found explain why that's the case, but I imagine it has to do with the "slave" part evolving to mean something more like "servant". Finally, that's composed of the prefix cum-, meaning "with" (from Proto-Indo-European kom, "next to"), and the root servus, meaning "slave" (from PIE serwo, "guardian").
Hello! I'm Adam Aleksic, a sophomore studying linguistics and government at Harvard University, where I founded the Harvard Undergraduate Linguistics Society. I also have disturbing interests in politics, vexillology, geography, board games, conlanging, and law.