What's the origin / etymology of the word hotel?

The Dariush Grand Hotel (هتل بزرگ داریوش) in the island of Kish, Iran

Olivier Simon of auxlang and sambahsa-mundialect knows, and now you know too:

(IE means Indo-European, by the way)

In Latin, "hostis" means "enemy", but the English correspondence is "guest"; so *ghostis may have meant "stranger" in IE (gost is "guest" in sambahsa).

In Latin, "hospes/hospitis" is "guest", and in Russian "gospodin" is "Sir". In IE, *ghostipotis meant the "chief of the strangers" (thus, in Sambahsa, "gospoti" is "alien" with a very polite meaning, while "tarnien" is stranger, from Chinese târen and Japanese tanin).

"Hospes" gave rise to "hospitable" and "hospitality" in modern Romance languages.

In the middle ages, monks used to provide some shelters for poor travelers, especially pilgrims. Those houses were called "hospitale".

In French, this low latin word (where the "h" was never pronounced, except in loanwords) turned to "hostel" then "hôtel". A "hôtel" designates at first any big house. A "hôtel particulier" is the private city home of wealthy people. A "hôtel de ville" is a city hall. And "hôtel" alone has the same sense it has kept in a lot of languages all around the world.

In the medical world, where Latin has long been a compulsory knowledge, the Latin original form "hôpital" has endured. But, the ancestors of modern hospitals were called in the Middle Ages "hôtel-dieu" ("God's hotel"!). It is common that in French, two different words from the same latin root are coexisting. Ex: "clavicule/cheville". "ausculter/écouter".... The "savant" form is closer to the latin outlook but, on the contrary, the "popular" form better respects the original latin stress pattern.