I've learned something new today.....

...at the local National Trust meeting. The speaker was Alaric Bond, author or nautical fiction and very knowledgeable indeed. One of his topics was well-used phrases from that world. We say "sleep tight", "swing a cat", "between the devil and the deep blue sea" and "freezing the balls off a brass monkey"  (not actually rude!) without always knowing what they mean.  "Slush fund" is one I hadn't thought of in nautical terms, but it means (from Wiki):

"The term slush fund was originally a nautical term: the slush was the fat or grease that was skimmed from the top of the caldron when boiling salted meat. Sometimes a cook would sell some of this fat to tallow makers, and the money was called his slush fund."