slush funds

/S L AH1 SH F AH0 N D Z/
noun
  1. 1

    Money stored for illegal or dishonest purposes.

    โ€œHe is said to have used his partyโ€™s slush fund to buy votes in the election.โ€

Source: https://en.wiktionary.org/wiki/slush%20fund, https://en.wiktionary.org/wiki/slush%20funds