To make worse; to diminish in quality or condition.
From dis- (reversal/opposite) + improve (from Old French emprendre, to undertake, later merged with 'prove' meaning to test/verify). The dis- prefix inverts the meaning of improve, creating its opposite.
While 'worsen' sounds more natural to modern ears, disimprove captures something unique: it emphasizes active *deterioration* rather than just being bad. Old English speakers loved this because it mirrored the structure of improve—they built opposites symmetrically, like linguistic mirror images.
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