stomach
The French word 'estomac' is used to refer to the stomach, an organ in the human body that is responsible for breaking down food and extracting nutrients. It is used in the same context as the English word 'stomach'. For example, 'J'ai mal à l'estomac' translates to 'I have a stomach ache' in English.
My stomach hurts.
In French, to express body ache, people use the phrase 'J'ai mal à l' followed by the part of the body that's hurting.
He has a stomach of steel.
The phrase 'estomac d'acier' metaphorically means that someone can eat anything without getting digestional problems, just as steel is a strong metal.
His stomach is rumbling.
The verb 'gargouille' is onomatopoeic, it imitates the sound your stomach makes when you're hungry. This phrase is used when somebody's stomach makes noises due to hunger.