To “climb on the bandwagon.”

Long ago, bands on the platforms of traveling wagons played music to announce a parade or political speech. To show their support, people would often jump onto the platform and join the band. Today, this idiom usually refers to someone who hopes to benefit from supporting another person's idea.

“Saved by the bell.”

In 17th-century England, a guard at Windsor Castle was accused of falling asleep at his post. He claimed he was wrongly accused and could prove it; he had heard the church bell chime 13 times at midnight. Townspeople supported his claim and he was not executed. Today we think of the bell that ends a round in boxing, often saving the boxer from injury, or the bell at the end of a class period, saving you from more work. Regardless, this idiom means rescue from a situation at the last possible moment.

“Bury the hatchet.”

Native Americans used to bury weapons to show that fighting had ended and enemies were now at peace. Today, the idiom means to make up with a friend after an argument or fight.

To “have a chip on one's shoulder.”

In nineteenth-century America, a boy who thought he was pretty tough would put a wood chip on his shoulder and dare anyone to knock it off. Today the idiom refers to anyone who is “touchy” or takes offense easily.