Take this medication 'on an empty stomach'. [=when your stomach is empty because you have not eaten for a time]
When I had the flu, just the thought of eating made me 'sick to my stomach'. [='nauseous']
She felt a flutter in 'the pit of her stomach' when he walked through the door.
(..) when all other creatures have fled because each guards a treasure: a single egg rested on the top of its feet and kept warm beneath the downy bulge of its stomach. There is no food and no water for them, and they will not see the sun again for four months. Surely no greater ordeal (..)2006 TvShow: Planet Earth Title: From Pole to Pole Season: 1 Episode 1