Noun.
Slang word for money, especially that obtained by criminal, illegal, or generally shady practices, e.g. selling
drugs, prostitution, slave trading. Can also mean a pay
check while working as an illegal immigrant. Used first by people in the black market and the Mafia.
Additionally, To 'give someone the mudsack' generally means to pay someone for doing something sneaky for you that you didn't want to do yourself.