slush fund
noun/ˈslʌʃ fʌnd/
/ˈslʌʃ fʌnd/
(disapproving)- a sum of money kept for illegal purposes, especially in politics
（尤指用于政治目的的）非法基金 Word Originmid 19th cent.: originally nautical slang denoting money collected to buy luxuries, from the sale of watery food known as slush.