the digestive system

stomachache

stom‧ach‧ache /ˈstʌmək-eɪk/ BrE AmE noun [uncountable and countable]
pain in your stomach or near your stomach
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THESAURUS
▪ stomachache pain in your stomach or near your stomach: He said he had a stomachache and didn't want to go to school. | I've got bad stomachache.
▪ indigestion pain or uncomfortable feelings that you get when your stomach cannot break down food that you have eaten: She frequently suffered from indigestion. | If I eat onions, they give me indigestion.
▪ food poisoning a stomach illness caused by eating food that contains harmful bacteria, so that you vomit: I got food poisoning while I was on holiday and had to spend the day in bed. | Two of the customers has to be taken to hospital with suspected food poisoning.
▪ nausea the feeling that you have when you think you are going to vomit: A feeling of nausea suddenly came over me.
▪ constipation the condition of having difficulty in getting rid of solid waste from your body: Do you suffer from constipation?
▪ diarrhoea British English, diarrhea American English an illness in which waste from the bowels is watery and comes out often: The main symptoms are diarrhoea and vomiting. | Some dairy products can cause diarrhoea.