" This Proto-Indo-European term ghosti (from which we get the words guest, host and ghost) referred to a kind of unspoken etiquette, a notion that on seeing strangers on the horizon, rather than choose to fell them with spears or sling-shots, instead we should take the risk of welcoming them across our threshold – on the chance that they might bring new notions, new goods, fresh blood with them.

Over time this word-idea evolved into the Greek xenia – ritualised guest–host friendship, an understanding that stitched together the ancient Mediterranean and Near Eastern worlds. "

― Bettany Hughes , Istanbul: A Tale of Three Cities