'Derail' definitions:

Definition of 'derail'

verb

Cause to run off the tracks; "they had planned to derail the trains that carried atomic waste"

verb

Run off or leave the rails; "the train derailed because a cow was standing on the tracks" [syn: derail, jump]

From: GCIDE

Derail \De*rail"\, v. t. [imp. & p. p. Derailed; p. pr. & vb. n. Derailing.] To cause to run off from the rails of a railroad, as a locomotive. --Lardner. [1913 Webster]