This phrase is used to describe a sum of money which is normally reserved for nefarious practices such as bribing or influencing officials.
The word slush first appears in the 17th century to describe half-melted snow and is still used in this context today. However, the word developed an alternative meaning describing the fat or grease from boiled meat, particularly in a nautical context. The Gentleman’s Magazine of 1756 uses the following phrase, “He used much slush (the rancid fat of pork) among his victuals”. I’m not sure that slush could ever have been very appetising, an impression vividly conveyed in William Thompson’s The Royal Navy-men’s Advocate of 1757, “Tars whose Stomachs are not very squeamish, can bear to paddle their Fingers in stinking Slush”.
But how did the word slush become to be associated with money? Well, conditions on board 18th century ships were such that even though the thought of slush might offend our modern sensitivities, it was clearly seen amongst the serving sailors to be something of a bonus. Indeed, they collected the fat as it oozed out of the cooking meat and once they landed at a port proceeded to sell it on to the local inhabitants. Although a lucrative practice, it was frowned upon by their superiors as is evidenced by William McNally in his Evils and Abuses in Naval and Merchant Service of 1839, “the sailors in the navy are allowed salt beef. From this provision, when cooked nearly all the fat boils off; this is carefully skimmed and put into empty beef or pork barrels, and sold, and the money so received is called the slush fund”. More positively, the Army and Navy Chronicle of the same year suggested that the money used from the sale of slush could be used to buy books for the crew, “To give men the use of such books as would best suit their taste, would be to appropriate what is their own, (viz.) the slush fund for the purchase of such works”.
So a slush fund was clearly a sum of money from the sale of fat from meat put to one side for future use. At that point, there was no connotation of it being used for illicit purposes. This contextual use seems to have sprung up only late in the 19th century and in an American political context. The Congressional Record of 1894 records the first usage in this context thus, “[Cleveland] was not elected in 1888 because of pious John Wanamaker and his $400,000 of campaign slush funds”.
So, there we have it – the original entrepreneurial origin of the phrase has now been totally subsumed by the taint of illegality. One can only surmise that the collected and preserved fat carefully garnered by the sailors on board ship stank to high heaven and the whiff gave rise to the association with something underhand or illegal as in the phrase, something fishy.
An interesting story behind a phrase that is now in common currency.