Tarnish
T'ARNISH, verb transitive
1. To sully; to soil by an alteration induced by the air, or by dust and the like; to diminish or destroy luster; as, to tarnish a metal; to tarnish gilding; to tarnish the brightness or beauty of color.
2. To diminish or destroy the purity of; as to tarnish reputation or honor.
T'ARNISH, verb intransitive To lose luster; to become dull; as, polished substances of gilding will tarnish in the course of time. Metals tarnish by oxydation.