The Collaborative International Dictionary of English v.0.48:
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]WordNet (r) 3.0 (2006):
derail v 1: cause to run off the tracks; "they had planned to derail the trains that carried atomic waste" 2: run off or leave the rails; "the train derailed because a cow was standing on the tracks" [syn: derail, jump]