If you are upset, you are unhappy or disappointed because something unpleasant has happened to you.

If something upsets you, it makes you feel worried or unhappy.

If events upset something such as a procedure or a state of affairs, they cause it to go wrong.

If you upset an object, you accidentally knock or push it over so that it scatters over a large area.

A stomach upset is a slight illness in your stomach caused by an infection or by something that you have eaten.