To make something lose its shine or brightness, or to damage someone's reputation or good name.
From Old French 'terniss-' (stem of ternir), possibly from Frankish origin. Originally meant to make dull or dim, extended metaphorically to reputation around the 16th century.
Silver tarnish is actually a chemical reaction (silver sulfide) forming a protective layer—nature's way of preventing deeper corrosion, which is why antique silver often survives centuries.
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