“Cache,” “cachet,” and “cash” sound alike, and are interconnected, but maybe not in the way you think.
The oldest in English, somewhat surprisingly, is “cash.”
From the Old French “casse,” for a box or chest, “cash” first showed up around 1595, The Oxford English Dictionary says, referring to both a box and its contents of coins or other monetary instruments.
Next up is “cachet,” pronounced “cash-EH.” Most of us know this to mean something that indicates status or prestige, as in “his new Lexus gives him more cachet.”
But “cachet” didn’t start out so grand. It actually derives from the French “cacher” meaning “to hide.” Around 1640, the OED says, it was used in the phrase “letter of cachet” to describe “a letter under the private seal of the French king, containing an order, often of exile or imprisonment.” Not necessarily a good thing. Around 1840, the OED says, the English novelist William Makepeace Thackeray used it to mean a “stamp” or “distinguishing mark.” It was a little over 40 years before it took on the sense of something that conferred prestige or approval.
“Cache,” as you might expect, is also from “cacher.” In the late 18th century, a “cache” was “a hole or mound made by American pioneers and Arctic explorers to hide stores of provisions, ammunition, etc.,” the OED says. And it was often spelled “cash.” By the mid-19th century, a “cache” was both the hiding place and the stuff being hidden.
So you can see that “cachet” and “cache” are closer cousins etymologically, while “cache” and “cash” seem more closely related by meaning. Of course, a “cache” of “cash” can confer great “cachet.” Share the wealth!