erosion

(noun) (geology) the mechanical process of wearing or grinding something down (as by particles washing over it). Synonyms: eroding, eating away, wearing, wearing away.

(noun) condition in which the earth's surface is worn away by the action of water and wind.

(noun) a gradual decline of something. Example: "After the accounting scandal there was an erosion of confidence in the auditors."

(noun) erosion by chemical action. Synonyms: corrosion, corroding.