tarnish

American Heritage® Dictionary of the English Language, Fourth Edition

1. v. To dull the luster of; discolor, especially by exposure to air or dirt.
2. v. To detract from or spoil; taint: a tragedy that tarnished our hopes.
3. v. To cast aspersions on; sully: slander that tarnished the senator's image.
4. v. To lose luster; become discolored.
5. v. To diminish or become tainted.
6. n. The condition of being tarnished.
7. n. Discoloration of a metal surface caused by corrosion or oxidation.
8. n. The condition of being sullied or tainted.

Century Dictionary and Cyclopedia

1. To diminish or destroy the luster of; sully; dull: used of an alteration induced by the air, or by dust or dampness; also, in mineralogy, to change the natural color or luster of the surface of: said chiefly of the metallic minerals. See tarnish, n., 2.
2. To give a pale or dim cast to, as to gold or silver, without either polishing or burnishing it.
3. Figuratively, to diminish or destroy the purity of; cast a stain upon; sully: as, to tarnish reputation.
4. Synonyms To dull, deface.
5. To lose luster; become dim or dull: as, polished substances or gilding will tarnish in the course of time.
6. n. A spot; a blot; the condition of being dulled or stained.
7. n. In mineralogy, the change in luster or color of the surface of a mineral, particularly one of metallic luster: usually due to slight alteration, but also in some cases to the deposition of a very thin film of some foreign substance. Thus, a freshly fractured surface of bornite soon gains a tarnish on exposure, becoming a bright purple color; it is hence often called variegated or purple copper ore; so also columhite crystals often show a brilliant steel-blue tarnish.
8. n. A coating.

Wiktionary

1. n. Oxidation or discoloration, especially of a decorative metal exposed to air.
2. v. To oxidize or discolor due to oxidation.
3. v. To soil, sully, damage or compromise

GNU Webster's 1913

1. v. To soil, or change the appearance of, especially by an alternation induced by the air, or by dust, or the like; to diminish, dull, or destroy the luster of; to sully.
2. v. To lose luster; to become dull.
3. n. The quality or state of being tarnished; stain; soil; blemish.
4. n. (Min.) A thin film on the surface of a metal, usually due to a slight alteration of the original color.

WordNet 3.0

1. n. discoloration of metal surface caused by oxidation
2. v. make dirty or spotty, as by exposure to air; also used metaphorically