You can keep it only after you give it to someone else. What is it?
Another possible answer:
Gaining a large amount of money from dubious sources can attract the attention of law enforcement agencies, who won't let you keep the money if they figure out that you earned it illegally. In order to keep the money, you have launder it. A common way of laundering money is giving it to someone (e.g. your wife) who's running an apparently legitimate business (e.g. a car wash). This person will mix this dirty money in with legitimate transactions, so it will ultimately appear as profit, which you can then keep since you happen to be the owner of this business.