In Garth Nix's book Sabriel, the titular character discovers a statue of a man. She is able to reanimate the man, she asks his name, and he replies "Touchstone." She replies something along the lines of "Touchstone? That's a fool's name." (I don't have the book with me so I can't quote it exactly.)
It is made obvious that it's not the man's original name, and it is also obviously (in both the book's world and ours) a dictionary word and not a "real" name... but why is it a fool's name specifically? Granted, dictionary words are not common as names, but it's not unheard of, and arguably "Touchstone" is a reasonably serious-sounding word to use.
Is there some in-world reason to say this? Given the book's fantasy trappings, is there a real-world cultural or historical reason that a fool would have or choose a word as a name?