A more thorough explanation:

Definition: Sponsio is a legal term from ancient Roman law. It refers to a promise or undertaking made by a citizen using a specific set of words with religious significance. This was the earliest form of stipulation, which was a type of contract.

One example of sponsio is when a Roman citizen would make a promise by saying, "Spondesne...?" which means "Do you promise...?" The other person would respond with "Spondeo," which means "I promise."

Another example is when a person would make a promise to the gods, such as "If I win this battle, I will sacrifice a goat to Jupiter." This was a type of sponsio that was considered binding and enforceable.

These examples illustrate how sponsio was a solemn and religiously significant promise made by Roman citizens. It was a way to create a legally binding agreement, and breaking a sponsio could have serious consequences.