Does a "Boolbazaur" exist?
It does not mean anything to you, therefore it only exists as a label.
Therefore, we can make the observation that something that is named exists only if it can be defined in terms of something that already exists.
Now this does not apply to the case where something is so hard to define on its own, so we try to define it by negating it's attributes to say what it isn't. This is how Jews define their creator, and Witness Consciousness affirming Hindus define