An old person whose mind has become weak; a person who dotes excessively or foolishly.
From Middle English, derived from 'dote' with the agent suffix '-ard' (like in 'drunkard'). The suffix '-ard' implies someone characterized by an excess of a quality.
King Lear is called a dotard in Shakespeare, and Trump supporters ironically called him one during his presidency—this insult has survived 600+ years by perfectly capturing one of our deepest fears: losing mental sharpness in old age.
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