A train is a number of carriages, cars, or trucks which are all connected together and which are pulled by an engine along a railway. Trains carry people and goods from one place to another.

A train of vehicles, people, or animals is a long line of them travelling slowly in the same direction.

A train of thought or a train of events is a connected sequence, in which each thought or event seems to occur naturally or logically as a result of the previous one.

The train of a woman's formal dress or wedding dress is the long part at the back of it which flows along the floor behind her.

If a process or event is in train or has been set in train, it is happening or starting to happen.

If something brings problems or difficulties in its train, the problems or difficulties occur as a natural or logical result of it.