How do you say "train" in Thai?

The term that translates to "train" in Thai is รถไฟ. This word specifically refers to the vehicle that travels on railway tracks, which is what most people commonly think of when they refer to a train.

The other options represent different forms of transportation. การขนส่ง generally translates to "transportation" or "transport," which is a broad category and does not specify a particular type of vehicle. รถบัส means "bus," referring to a different mode of public transport. สนามบิน translates to "airport," which is a place primarily associated with air travel, not ground travel like trains. Thus, รถไฟ is the accurate answer for "train."