As a verb, it means to disturb or knock something over, or to make someone unhappy or worried. As an adjective, it describes feeling unhappy or emotionally disturbed; as a noun, it can mean an unexpected defeat.
From 'up' + 'set' (to place), originally meaning 'to overturn' in the 1400s. The emotional sense grew later from the idea of someone’s inner balance being knocked over.
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