Pronunciation: (dē-rāl'),[key] —v.t. 1. to cause (a train, streetcar, etc.) to run off the rails of a track.
2. to cause to fail or become deflected from a purpose; reduce or delay the chances for success or development of: Being drafted into the army derailed his career for two years.
—v.i. 1. (of a train, streetcar, etc.) to run off the rails of a track.
2. to become derailed; go astray.
—n. a track device for derailing rolling stock in an emergency.