Etymology
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derail (v.)

1850 (Dionysius Lardner, "Railway Economy"), in both transitive and intransitive senses, "cause to leave the rails or run off the tracks; to run off the rails or tracks," from French dérailler "to go off the rails," from de- (see de-) + railler (see rail (n.1)). Related: Derailed; derailing.

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Definitions of derail

derail (v.)
cause to run off the tracks;
they had planned to derail the trains that carried atomic waste
derail (v.)
run off or leave the rails;
the train derailed because a cow was standing on the tracks
Synonyms: jump
From wordnet.princeton.edu