TRIVIAL PURSUITS: From where did the term ‘slush fund’ originate?

But, from where did the term originate?

In the mid-18th century, salty fat or grease left over from the pig or cow meat that boiled nearly every night for dinner on ships at sea was saved by cooks. When in port, the ‘slush’ would be sold to candle and soap makers. The money usually helped provide extras that the crew couldn’t otherwise afford, so it was called their ‘slush fund.’

Though it has a negative connotation, it could mean money put aside for various expenses.