Let's talk about waiver first. That extra i - which maybe you think isn't that important in the grand scheme of things - is a clue as to the correct usage of the word. But, this trick relies on another trick: the difference between insure and ensure.
Insure deals with insurance that is purchased: car, life, dental, medical - you get the idea.
Ensure deals with making certain of something in the future. I want to ensure that you will know the difference between waiver and waver, for example. (I certainly would not want to insure you know the difference - I am not sure who would carry that policy!)
Ok, now that we have that settled, you can think of the i in waiver as something related to insurance, which is related to official or legal matters. The only definition of waiver is a formal written statement of relinquishment (sounds lawyer-ish, doesn't it?). It's a noun, which also clues you in that you can't use it as a verb. Waive is the verb form to use if you are going to waive your rights. (I swear, I have no personal knowledge of waiving my rights - it's all from Law & Order!!)
But waver - now that's a word with action! It can mean:
Pause or hold back in uncertainty or unwillingness
Be unsure or weak
Move hesitatingly, as if about to give way
Move or sway in a rising and falling or wavelike pattern
Move back and forth very rapidly
Sway to and froGive off unsteady sounds, alternating in amplitude or frequency
It can also be a noun - someone who communicates by waving, the act of pausing uncertainly, or the act of moving back and forth.
So, next time you have your character's voice waver, be sure they are not waiving their rights in the criminal justice system.