de·rail / dēˈrāl/ • v. [tr.] (usu. be derailed) cause (a train or trolley car) to leave its tracks accidentally: a train was derailed after it collided with a herd of cattle. ∎  [intr.] (of a train or trolley car) accidentally leave the tracks: the trolley cars had a tendency to derail on sharp corners. ∎  [tr.] fig. obstruct (a process) by diverting it from its intended course: the plot is seen by some as an attempt to derail the negotiations.DERIVATIVES: de·rail·ment n.

derail XIX. — F. dérailler, f. DE- 2 + rail RAIL 2.