Apparently a central part of our bodies.
If you believe the pronunciation on some TV commercials about our STOMACH, you have good reason to say "What…where…why is a stummick?" Let's begin pronouncing it the way it's spelled…s-t-o-m-a-c-h. Easy peasy.
The only thing worse than this aberrant pronunciation is any long-running soap opera sarcastically called "As the Stomach Turns".
There is no such thing as a "stummick", as far as I know.