“Lunatic” means idiotic and crazy, and if a train is called a “Lunatic Express”, the reader expects conditions on the train to be chaotic and almost dangerous

“Lunatic” means nighttime, and if a train is called a “Lunatic Express”, the reader expects the train to travel through the night

“Lunatic” means mentally unstable, and if a train is called a “Lunatic Express”, the reader expects it to be full of people that are crazy