/dee rayl"/ , 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.
3. (of a train, streetcar, etc.) to run off the rails of a track.
4. to become derailed; go astray.
n.
5. a track device for derailing rolling stock in an emergency.
[ 1840-50; dérailler, equiv. to dé- DIS- 1 + -railler, v. deriv. of rail RAIL 1 ( ]