upsetupsetupsetsupsetting2adjective1unhappy or worried: The children were very upset when their dog died.2ill: I've got an upset stomach.▶ upsetupsetupsetsupsettingnounan illness in your stomach: Sara has got a stomach upset. upsetupsetupsetsupsetting1verb (upsets, upsetting, upset, has upset)1to make somebody feel unhappy or worried: You upset Tom when you said he was fat.2to make something go wrong: The bad weather upset our plans for the weekend.3to knock something so that it turns over and things fall out: I upset a glass of wine all over the table.