A feeling of worry, discomfort, or anxiety about something; not being at ease or relaxed.
From 'un-' (negation) plus 'easiness' (from 'ease,' from Old French 'aise' meaning comfort). The chain of word formation shows how English builds complex emotions from simple ones.
Notice how many mental states are just 'un-' + a physical comfort word: unease, discomfort, unrest. Our language treats emotional disturbance as the opposite of physical comfort, which is actually pretty accurate to how stress works!
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