Caboose

The crossword question probably asks for a word that means the back of a train, and the answer is “caboose.” A caboose is the last car on a freight train, and it is used by the crew to monitor the train and provide living quarters. The caboose’s location at the end of the train means that it is indeed located in the rear of the train. Therefore, the clue “Caboose is REAR” means that the word “rear” can be used as a synonym for “caboose,” as the caboose is located at the rear of the train.