- The definition of breakneck is something that is moving really, dangerously fast.
Driving at 100 miles per hour is an example of driving at breakneck speed.
One car passes another at breakneck speed.Licensed from iStockPhoto
Used by arrangement with John Wiley & Sons, Inc.
- Dangerously fast: a breakneck pace.
- Likely to cause an accident: a breakneck curve.