The word should be prounded “cash”, to rhyme with “stash”, if you need a mnemonic; (n. ‘hidden store’, or v. ‘to hide’) The word is French, meaning something like “to conceal”, or “place of concealment”.

I first heard it in high school, it was the hiding place where French Canadian wilderness trappers, the voyageurs, hid their supplies to protect them from animals and thieves out in the wilderness. They would cache their gear and trap an area out, then cache the furs and move what was left of their supplies to another area they planned to work. Yes, we actually learned stuff like that in my Florida high school.

Lately, I’ve been hearing Americans prounounce it “kash-ay”, which really irritates me. It sounds like cop-speak, y’know, “We responded to the vicinity of the altercation and found the subject contravening a breach of the peace” when “he was causing a disturbance” would do just fine.

Normally, I don’t mind when people mispronounce fancy words. It shows that they have read and understood words not commonly used in their day-to-day conversation, which is to their credit.
But “cashay” really rubs me the wrong way, for some reason. It’s like they’re trying to show off and only make a fool of themselves. It bugs me almost as much as substituting “axe” for “ask”.