Other forms: buckled up; buckling up; buckles up
When you pull your seat belt over your shoulder and clip it securely across your lap, you buckle up. Don't forget to buckle up before you drive your bumper car into the fray!
You can buckle up anything with a buckle — like your shoes, backpack, or belt — but the term usually refers to a seat belt. When you're learning to drive, you'll be told to buckle up before putting the car in gear. This North American phrase can also be used figuratively to mean "get ready." A melodramatic math teacher might say, "Buckle up, class, this is going to be the hardest quiz of your life!"