We’ve fallen “behind” with our word origins posts lately, so let’s get to the “bottom” of things. Make sure to read to the “end”!
Linguists say this one only dates back about 50 years. It’s also a specifically American slang term. It’s an all-American Englishification and shortening of tukhus, or tokhes, which is a Yiddish slang term that means “the buttocks.” That, in turn comes from the Hebrew word tahath, which means, more broadly “underneath.”
It means a bunch of things around the English-speaking world. Because it’s widely used to refer to one’s underside, it’s not used as a name or nickname much anymore — as in famous entertainer Fanny Brice, or Ingmar Bergman’s epic film Fanny and Alexander — but in this way, it’s short for Frances or Francis. Unfortunately for those named Fanny, in the 1920s in England and Australia the word came to be a vulgar reference to the female anatomy. As the word made its way to America, it came to refer to the rear end instead…and its crassness softness.
This one similarly has a handful of different meanings. Most notably, old timey pirates use it to describe their loot or plunder, which derives from some old European language words that mean “trade” and “distribute.” But booty is also used to refer to the anatomical bottom…which doesn’t have anything to do with pirates. Linguists aren’t totally sure how this usage came about, but many think it’s a derivative of “body,” pronounced with a pronounced Southern accent.
How come the ridiculous prank of exposing one’s bare buttocks out of a car window (or in public in some other way) is called “mooning”? Is it because the crumb-bums who do it do it under the cover of night? Nope, it’s just one of many English-language associations between the moon and the human backside. Linguists say that writers compared the round shape of one object to the other as early as the 1740s, while “mooning” itself is an obscure phrase dating to the 1600s that means “expose to moonlight.” The 20th century teenage goof married those two meanings.