to fasten a strap that holds you in your seat in a vehicle or aircraft.

Four out of five children are not correctly buckled up.

The pilot asked the passengers to buckle up because we were flying through a storm system.

• when back is turned
• when hell freezes over
• When in Rome .
• When in Rome do as the Romans do.
• when it comes to the crunch
• when push comes to shove
• when ship comes in
• when someone's back is turned
• when someone sneezes, someone catches a cold
• when someone sneezes, something catches a cold
• when someone was a mere twinkle in father's eye
• when someone was a mere twinkle in their father's eye
• when someone was a twinkle in father's eye
• when someone was a twinkle in their father's eye
• when something sneezes, someone catches a cold
• when something sneezes, something catches a cold
• When the cat's away .
• When the cat's away the mice will play.
• when the chips are down
• when the dust settles
• when the going gets rough
• when the going gets tough
• when the spirit moves
• when the spirit moves you
• when was a mere twinkle in father's eye