A universal definition of “chair” is pretty hard to pin down, too…
https://en.wikipedia.org/wiki/Ontology
Or: just try, then try your best to find ways your definition fails. You should find it challenging, to put it mildly, to create a bulletproof definition, if you’re really looking for angles to attack each definition you can think of. They’ll end up being too broad, or too narrow. Or coming up short on defining when exactly a non-chair becomes a chair, and vice-versa, or what the boundaries of a chair are (where chairness begins and ends).
And if that one is tricky…
So I'm asking how you define a definition as "too broad".
Because my perspective is that definitions that are in fact too broad are unimportant because no one uses them.
Universal definitions? Extremely hard.