What is the Thai word for "bus"?

The Thai word for "bus" is indeed "รถบัส," pronounced as "rot bas." This term combines the word for "vehicle" (รถ, or "rot") with a transliteration of the English word "bus," showcasing how Thai often adapts foreign terminology into its lexicon.

The other options reference different modes of transportation or concepts. "รถไฟ" (rot fai) means "train," which distinctly refers to rail transport. "การขนส่ง" (kan khon song) translates to "transportation" in general, and while it encompasses buses, it does not specify one. Lastly, "ห้องโดยสาร" (hong samut) translates to "passenger room" or "passenger cabin," which is more related to the interior of a vehicle rather than a specific mode of transport. Thus, "rot bas" accurately identifies the specific vehicle known as a bus.