Wiktionary
you-know-what
pron. Something whose name one does not want to mention, but which is known to the person to whom one is speaking.
Usage examples of "you-know-what".
Or,” he dropped his voice to a whisper, “d’you reckon you already know where the You-Know-Whats are?
My wightish friend here did not, like the You-Know-What, the Prince of Waterhorses, tear its victims to pieces—after it rid itself of its burden, it used to set up a great nicker and a laugh and next be seen galloping and plunging off into the distance.