Extremely tired, having no energy left; or having used something up completely.
From Latin 'exhaustus,' past participle of 'exhaurire' meaning to draw out or empty. 'Ex-' means out, and 'haurire' means to draw or drain.
Exhausted literally means 'drained out'—you're running so empty you've 'hauled out' all your energy! The same root gave us 'exhaust pipes' that blow out gases, showing how one root describes complete emptying.
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