Longman Dictionary of Contemporary English
Wiktionary
alt. A restraining belt attached to a vehicle seat which is fastened around passengers and which is intended to keep an occupant in place so as to avoid injuries in accidents where the occupant could be thrown against a solid object. n. A restraining belt attached to a vehicle seat which is fastened around passengers and which is intended to keep an occupant in place so as to avoid injuries in accidents where the occupant could be thrown against a solid object.
WordNet
n. a safety belt used in a car or plane to hold you in your seat in case of an accident
Wikipedia
A seat belt, also known as a safety belt, is a vehicle safety device designed to secure the occupant of a vehicle against harmful movement that may result during a collision or a sudden stop. A seat belt functions to reduce the likelihood of death or serious injury in a traffic collision by reducing the force of secondary impacts with interior strike hazards, by keeping occupants positioned correctly for maximum effectiveness of the airbag (if equipped) and by preventing occupants being ejected from the vehicle in a crash or if the vehicle rolls over. When driving, the driver and passengers are travelling at the same speed as the car. If the car suddenly stops or crashes, the driver and passengers continue at the same speed the car was going before it stopped. A seatbelt applies an opposite force to the driver and passengers to prevent them from falling out or making contact with the interior of the car. Seatbelts are considered as Primary Restraint Systems (PRS) as they play a vital role in occupant safety.
Usage examples of "seat belt".
I unfastened my seat belt, rose, glanced at Maggie and Belinda without expression or recognition and headed for the exit while the plane was still moving, a manoeuvre frowned upon by the airline authorities and certainly, in this case, by other passengers in the plane whose expressions clearly indicated that they were in the presence of a big-headed and churlish boor who couldn't wait to take his turn along with the rest of long-suffering and queueing mankind.