Working with Stuff Mom Never Told You, I often have breasts on the brain. Lately, I've particularly been pondering the sexualization of women's cleavage - not to be confused with men's "he-vage"' - in Western culture. According to Marilyn Yalom's History of the Breast, women's fashions favored décolletage throughout the Renaissance, but today it's far more fraught with innuendo. Tracking down succinct explanations for our collective obsession with breasts and cleavage in more recent times has been a challenge, and surprisingly, one of the hardest questions to answer on this breast quest is where the slang term "boob" came from.
The Oxford English Dictionary (via Straight Dope) says people in the 16th century first started using "boob" and "booby" as insults for being stupid. That likely sprang from the Latin balbus, meaning stammering, which then gave way to the Spanish bobo for stupid. (On a side note, this settles why we refer to mind-numbing TVs as "boob tubes").
So did we make a linguistic jump from dunces to D-cups? Grammarphobia, referencing the OED, cites the first instance of "booby" in reference to breasts in Henry Miller's 1934 Tropic of Cancer: "She was lying on the ground with her boobies in her hands." And would we expect any less from ToC?
But Miller didn't make up the anatomy slang. The Online Etymology Dictionary dates the U.S. usage back to 1929 and traces it to the Latin puppa, or little girl. According to the site, puppa begat the German bubbi, which begat the English bubby. And Merriam Webster defines "bubby" as a vulgar slang that originated around 1675. It's conceivable then that over time, "bubby" evolved into "booby" and was shortened to "boob".
Initially, I assumed the etymology of boob would lead to the dunce insult, but instead it refers to little girls. And that calls to mind another slang word: skeevy.