to fasten your seat belt (= a belt worn by a passenger in a vehicle); Used to tell someone to get ready for something intense, difficult, long, or surprising that is about to happen.
Oxford79% of films
to fasten your seat belt (= a belt worn by a passenger in a vehicle)
Editorial21% of films
Used to tell someone to get ready for something intense, difficult, long, or surprising that is about to happen.
Yeah. Buckle up, babe. [chuckles]
Definitions from the Oxford Advanced Learner's Dictionary, 9th edition