Attrition

Attrition

Dictionary.com defines the word in the following ways:
Attrition–noun 1. a reduction or decrease in numbers, size, or strength: Our club has had a high rate of attrition because so many members have moved away. 2. a wearing down or weakening of resistance, esp. as a result of continuous pressure or harassment: The enemy surrounded the town and conducted a war of attrition. 3. a gradual reduction in work force without firing of personnel, as when workers resign or retire and are not replaced. 4. the act of rubbing against something; friction. 5. a wearing down or away by friction; abrasion.