A more thorough explanation:

A compounder is someone who:

1. settles a dispute or makes a composition
2. knows about a crime committed by someone else and agrees not to prosecute in exchange for a reward

1. John and Jane were arguing about who should get the last slice of pizza. Their friend Tom acted as a compounder and suggested they split the slice in half so they could both have some.

2. The police offered a reward for information about a robbery. A compounder came forward and said they knew who did it, but only if they received a portion of the reward money.

These examples illustrate the two different meanings of the term "compounder." In the first example, Tom acted as a mediator or peacemaker to resolve a dispute. In the second example, the compounder is someone who withholds information about a crime in exchange for a reward, which is illegal and unethical.