Derailment (noun)

1. An accident in which a train or other vehicle comes off the tracks.
2. The act of causing a plan or process to fail or be disrupted.

Origin:

From the verb "derail" which means to cause a train or other vehicle to come off the tracks.

Examples:

1. The derailment caused major delays for commuters.
2. The derailment was caused by a broken rail.
3. The derailment resulted in several injuries and deaths.
4. The meeting was going well until a heated argument caused a derailment of the discussion.
5. His promotion was on track until a scandal caused a derailment of his career.