slush fund 

A sum of money set apart for discretionary and/or undocumented spending, often fraudulent, illegal, or dishonest.

News Junkie: Our governments is widely known for unaccountable slush funds built up to funnel money to their friends.
Innocent Kid: Are you serious? I've never heard about that. How this could ever happen?

slush fund by humblepiece June 2, 2017

Slush Fund 

A secret stash of money usally used for the most part in emergencies only.

I used my locker to hold my slush fund not my books.

Slush Fund by Mic February 9, 2004

slush fund 

Refers to the "reserve" of half-melted snow that Calvin keeps handy for making into sloppy "cannon balls" to lob at Susie anytime he catches sight of her during the winter months.

Susie feels confident about venturing outside only after the snow has disappeared in the Spring, when she can be sure that Calvin's slush fund will be completely melted.

slush fund by QuacksO March 7, 2019