What is the meaning of Tarnish?

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

To oxidize or discolor due to oxidation.

To compromise, damage, soil, or sully.

To lose its lustre or attraction; to become dull.

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

Source: wiktionary.org