tarnish

A dull coating or discolouration that forms on the surface of metal.

"There was a slight tarnish on the old brass."

A blemish or stain that damages someone's good reputation or character.

"The scandal left a tarnish on his name."

To damage or spoil the good reputation or image of someone or something.

"His past actions could tarnish his political career."

To make or become dull, discoloured, or less bright, especially metal.

"The silver will tarnish if not polished regularly."