Definition of "derailment"

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.

1961 November, “Talking of Trains: Derailment near Holmes Chapel”, in Trains Illustrated, page 652

But when the second stage set in, in which man became preponderantly self-conscious, he inevitably set about deflecting sex-activities to his own private pleasure and advantage; he employed his budding intellect in scheming the derailment of passion and desire from tribal needs and, Nature's uses to the poor details of his own gratification.

1920, Edward Carpenter, Pagan and Christian Creeds, New York: Harcourt, Brace and Co., published 1921, page 186