tarnish (
http://definr.com/tarnish)
n : discoloration of metal surface caused by oxidation
v : make dirty or spotty, as by exposure to air, of metals; also
used metaphorically: "The silver was tarnished by the
long exposure to the air"; "Her reputation was sullied
after the affair with a married man" [syn:
maculate,
sully,
defile]