tar·nish 
(tärnĭsh)
(tärnĭsh)v. tar·nished, tar·nish·ing, tar·nish·es
v. tr.
1. To dull the luster of; discolor, especially by exposure to air or dirt: Being in the ground for so long tarnished the old coins.
2.
a. To detract from or spoil: a tasteless meal that tarnished an otherwise pleasant evening.
b. To bring disgrace to; sully: a scandal that tarnished his reputation.
v. intr.
1. To lose luster; become discolored: a metal that tarnishes quickly.
2. To become less enjoyable or estimable: Her admiration for the movie's producer quickly tarnished.
n.
1. The condition of being tarnished: no sign of tarnish on the frame.
2. A film or layer of discoloration on a metal surface caused by corrosion or oxidation.
3. The condition of being disgraced or made less estimable: the tarnish on his reputation.
[Middle English ternishen, from Old French ternir, terniss-, to darken, tarnish, from Frankish *tarnjan; see dher- in the Appendix of Indo-European roots.]
tarnish·a·ble adj.