TRAIN

• train [countable]
• 1

  railway

  a set of several carriages that are connected to each other and pulled along a railway line by an engine
• COLLOCATIONS 
• by train (=travelling on a train)
• catch/get a train
• get on/board a train
• get off a train
• take a train (=travel using a train)
• wait for a train
• miss a train (=be too late to get on a train)
• a train pulls into/out of a station
• freight/goods train (=a train that carries goods)
• passenger train (=a train that carries people)
• commuter train (=a train that people going to work use)
• train journey/ride
• train fare (=the money you pay for a train journey)
• train to
• the train to Munich
• We went all the way to Inverness by train.
• It's more relaxing to go by train.
• You need to catch the early train to Bruges.
• We were finally given instructions to board the train.
• At Richmond a lot of people got off the train.
• I took the first train home.
• a lone commuter waiting for a train late at night
• I missed the train and had to wait another two hours.
• The train pulled out of Paddington, and soon we were racing towards Wales.
• They would go on long train journeys together.
• ➔ boat train
• 2

  series

   a train of something

  a series of events or actions that are related:
• The decision set off a train of events which led to his resignation.
• 3

   train of thought

  a related series of thoughts that are developing in your mind:
• The phone interrupted my train of thought.
• I've lost my train of thought.
• 4

   bring something in its train

  formal if an action or event brings something in its train, that thing happens as a result of it:
• a decision that brought disaster in its train
• 5

   set something in train

  British English formal to make a process start happening:
• Plans to modernize have been set in train.
• 6

  people/animals

  a long line of moving people, animals, or vehicles:
• a camel train
• 7

  dress

  a part of a long dress that spreads out over the ground behind the person wearing it:
• a wedding dress with a long train
• 8

  servants

  a group of servants or officers following an important person, especially in the past

Definition from the Longman Dictionary of Contemporary English
Advanced Learner's Dictionary.