—v.t. 1. to overturn: to upset a pitcher of milk. 2. to disturb mentally or emotionally; perturb: The incident upset her. 3. to disturb or derange completely; put out of order; throw into disorder: to upset a system; to upset a mechanism; to upset an apartment. 4. to disturb physically: It upset his stomach. 5. to defeat or overthrow an opponent that is considered more formidable, as in war, politics, or sports.
6. Metalworking.to thicken the end of (a piece of heated metal) by hammering on the end against the length of the piece.
—v.i. to become upset or overturned.
—n. 1. an upsetting or instance of being upset; overturn; overthrow.
2. the defeat of a person, team, etc., that is considered more formidable.
3. a nervous, irritable state of mind.
4. a disordered or confused arrangement.
5. Metalworking. a. a tool used for upsetting.
b. something that is upset, as a bar end.
—adj. 1. overturned: an upset milk pail. 2. disordered; disorganized: The house is upset. 3. distressed; disturbed: She had an upset stomach. He is emotionally upset. 4. Archaic.raised up.