derailment

From French déraillement.

derailment (countable and uncountable, plural derailments)

1. (rail transport) The action of a locomotive or train leaving the rails along which it runs.
   • 1961 November, “Talking of Trains: Derailment near Holmes Chapel”, in Trains Illustrated, page 652:

     The length ganger saw the train passing with the van derailed and promptly telephoned the Sandbach signalman, who restored his signals to danger, but not in time to stop the train before the final derailment occurred.

2. (psychiatry) A pattern of discourse (in speech or writing) that is a sequence of unrelated or only remotely related ideas.
3. An instance of diverting a conversation or debate from its original topic.

• derailment on Wikipedia.Wikipedia
• “derailment”, in Lexico, Dictionary.com; Oxford University Press, 2019–2022.

• delirament, terminaled