Mental or brain fatigue; weakness or exhaustion of the mind or mental abilities, a condition once thought to be caused by overuse of the brain.
From cerebrum (brain) plus Greek asthenia (weakness). This medical term emerged in the 19th century to describe mental fatigue, now considered outdated.
In the 1800s, doctors actually believed too much mental work could cause 'brain weakness'—rich people who thought too hard were told to rest at spas; today we call it stress or burnout.
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