mid-15c., "to set up, fix," from up (adv.) + set (v.). Similar formation in Middle Dutch opsetten "set up, propose," German aufsetzen. Modern sense of "overturn, capsize" (1803) is that of obsolete overset. In reference to the stomach, from 1834. Meaning "to throw into mental discomposure" is from 1805. Related: Upsetting.