corrosion

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The act or process of corroding.
• noun The condition produced by corroding.
• noun A substance, such as rust, formed by corroding.

from The Century Dictionary.

• noun In geology, the solution and removal of rocks, usually in water; the eating away by fusion and absorption of a solid mass of rock or of a mineral which is inclosed in a molten magma.
• noun Literally, the act or process of eating or gnawing away; hence, the process of wearing away, disintegrating, or destroying by the gradual separation of small parts or particles, especially by the action of chemical agents, as acids: often used figuratively of the destructive influence of care, grief, time, etc.

from the GNU version of the Collaborative International Dictionary of English.

• noun The action or effect of corrosive agents, or the process of corrosive change.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The act of corroding or the condition so produced.
• noun A substance (such as rust) so formed.
• noun chemistry Erosion by chemical action, especially oxidation.
• noun by extension The gradual destruction or undermining of something.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a state of deterioration in metals caused by oxidation or chemical action
• noun erosion by chemical action