As a Noun: 1. A strap attached to a seat in a car or an aeroplane. You fasten it across your body in order to prevent yourself being thrown out of the seat if there is a sudden movement. English = seat belt. 2. A piece of metal or plastic attached to one end of a belt or strap, which is used to fasten it. English = buckle. As a Verb or Adjective: 1. To put on a belt, to fasten a belt, to buckle up a belt. 2. To put on a seat belt, to fasten a seat belt, to buckle up a seat belt.