To free someone from a heavy load, responsibility, or emotional weight; to talk about something that has been troubling you.
From prefix 'un-' (not, reverse) combined with 'burden' (from Old French 'borde,' related to 'load'). The emotional meaning developed alongside the physical one, meaning to free someone's mind of worry.
The emotional meaning of 'unburden'—sharing your problems to relieve stress—became psychologically validated in the 20th century, but people have understood that talking lightens emotional weight for thousands of years.
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