attrition

1. Grinding down or wearing away by friction. (countable, uncountable)
2. The wearing of teeth due to their grinding. (countable, uncountable)
3. A gradual reduction in number. (countable, uncountable)
4. A gradual, natural reduction in membership or personnel, as through injury, incapacitation, retirement, resignation, or death. (countable, uncountable)
5. The loss of participants during an experiment. (countable, uncountable)
6. The loss of a first or second language or a portion of that language. (countable, uncountable)
7. Imperfect contrition or remorse. (countable, uncountable)

Plural attritions