deboard vs detrain

deboard

verb
  • To exit a form of transportation such as a boat, ship, airplane, trolley, streetcar or spaceship. 

detrain

verb
  • To exit from a train; to disembark 

  • to reduce one's training, particularly during the offseason, in preparation for a cycle of retraining. 

  • to remove a passenger or passengers from a train; to evacuate passengers from a train. 

How often have the words deboard and detrain occurred in a corpus of books? (source: Google Ngram Viewer )