Attrition

Attrition-n
1-the wearing away of a surface, typically by friction or abrasion
2-the gradual wearing away of morale and the powers of resistance by persistent attacks
3-the gradual reduction of the size of a workforce by not replacing personnel lost through retirement or resignation
4-remorse for sin typically engendered by the fear of damnation

Synonyms
abrasion
slow destruction
erosion
wear and tear
eating away
gnawing away
wearing away
grinding down