adj

• (of a person, predicative only) Angry, distressed, or unhappy.
  "He was upset when she refused his friendship."
• (of a stomach or gastrointestinal tract) Feeling unwell, nauseated, or ready to vomit.
  "His stomach was upset, so he didn't want to move."

noun

• (uncountable) Disturbance or disruption.
  "My late arrival caused the professor considerable upset."
• (countable, sports, politics) An unexpected victory of a competitor or candidate that was not favored to win.
  "But it is probably the biggest upset for the away side since Ronnie Radford smashed a famous goal as Hereford defeated Newcastle 2-1 in 1972."
• (automobile insurance) An overturn.
  ""collision and upset": impact with another object or an overturn for whatever reason."
• (mathematics) An upper set; a subset (X,≤) of a partially ordered set with the property that, if x is in U and x≤y, then y is in U.

verb

• (transitive) To make (a person) angry, distressed, or unhappy.
  "I’m sure the bad news will upset him, but he needs to know."
• (transitive) To disturb, disrupt or adversely alter (something).
  "Introducing a foreign species can upset the ecological balance."
• (transitive) To tip or overturn (something).
  "1924, W. D. Ross translator, Aristitle, Metaphysics, Book 1, Part 9, The Classical Library, Nashotah, Wisconsin, 2001. But this argument, which first Anaxagoras and later Eudoxus and certain others used, is very easily upset; for it is not difficult to collect many insuperable objections to such a view."
• (transitive) To defeat unexpectedly.
  "Truman upset Dewey in the 1948 US presidential election."