buckle up

verb3

1. •
   To fasten with a buckle.

   • It was eight o'clock to-morrow evening when I buckled up my travelling writing-desk in its leather case, paid my Bill, and got on my warm coats and wrappers. — 1855
2. •
   To fasten one's seat belt or safety belt.

   • Buckle up every time you drive somewhere in a car, and make sure your passengers buckle up, too.
3. •
   To get ready, to prepare oneself.

   • So buckle up for what's coming, readers! — 2019