Monosyllable — For most of the eighteenth and nineteenth centuries, this was the most common slang euphemism for one of the most dreaded of the four-letter words, i.e., cunt. ‘Mrs. Jewkes took a glass and drank [a toast to] the dear monosyllable. I don’t understand that word, but I believe it is baudy.’ (Henry Fielding, Shamela, 1761)”

—from Hugh Rawson, Dictionary of Euphemisms and Other Doubletalk