upset 1adjective up‧set1 1 [not before noun]unhappy and worried because something unpleasant or disappointing has happened upset by/about/at etc She was really upset about the way her father treated her. upset that Debbie was upset that he didn't spend more time with her. 2 be upset with somebody if you are upset with someone, you are angry and annoyed with them: You're not still upset with me, are you? 3 upset stomach MIan illness that affects the stomach and makes you feel sick