Merriam-Webster's Collegiate® Dictionary, 11th Edition
UPSET
I. verb (-set; -setting)
Date: 1677
transitive verb to thicken and shorten (as a heated bar of iron) by hammering on the end ; swage , to force out of the usual upright, level, or proper position ; overturn ,
3. to trouble mentally or emotionally ; disturb the poise of , to throw into disorder, invalidate , to defeat unexpectedly , to cause a physical disorder in, intransitive verb to become overturned, see: discompose upsetter noun
II. noun
Date: 1804
an act of overturning ; overturn ,
2. a. an act of throwing into disorder ; derangement, a state of disorder ; confusion , an unexpected defeat,
3. a minor physical disorder , an emotional disturbance ,
4. a part of a rod (as the head on a bolt) that is upset, the expansion of a bullet on striking,
III. adjective
Date: 1805
emotionally disturbed or agitated