Oxidation or discoloration, especially of a decorative metal exposed to air.

(intransitive) To oxidize or discolor due to oxidation.

(transitive) To compromise, damage, soil, or sully.

(intransitive, figurative) To lose its lustre or attraction; to become dull.

(copyright law) To use a sign, image, expression, etc. sufficiently close to a trademarked one that it brings disrepute to it.