Ever wonder why money set aside....

"Slush" referred to refuse fat and grease from a cook's galley.  In the British navy many years ago a ship's slush was often sold as a lubricant, with the proceeds being used to buy small luxuries for the ship's enlisted men.  The money resulting from these sales was called the ship's "slush fund".

 

Later the term was applied to a fund set up for similar purposes but contributed to by the enlisted men.  Today, of course, the term refers to money to be used for bribery, political payoffs, and other corrupt practices.