by nature you fear me, most want to learn, once learn I no longer exist. what am I?

The rich need me, the poor have me. If you eat me, you'll die.

I am an odd number. Take away a letter and I become even. What number am I?

I am made when lips refuse to open, kept alive by the teeth that lock the door. I vanish the moment I’m named, yet if you bury me I only grow. I have no weight, no colour, no sound, and still I can topple kings and drown a town. What am I?

I’m kept by those who lose me, lost by those who keep me. Spoken when silent, silenced when spoken. I’m the answer to no question, yet questioned by every answer. Found in the void, gone in the crowd. I shape thought without form. What am I?