buckle up

verb

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.”

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!”