A pact is a formal agreement or promise between two or more people or groups. When you make a pact with your friend to both study for an hour every night, you're making a serious commitment to each other. The word suggests something more binding than a casual promise: pacts have weight and importance.

Throughout history, pacts have shaped the world. Nations sign pacts to end wars or form alliances. The famous Mayflower Compact was a pact among the Pilgrims about how they would govern themselves in the New World. During World War II, countries formed pacts that helped determine which side they would fight on.

The word carries a sense of solemnity and mutual obligation. When friends make a pact to stand up for each other against bullies, they're declaring their loyalty. When siblings make a pact not to tell their parents about a broken lamp, they're bound by that secret agreement (even if keeping it might not be the wisest choice).

A pact is something you make or sign with others. Breaking a pact often damages trust and relationships because the other person was counting on you to keep your word.