くさる， 腐る
1. to rot, to go bad, to decay, to spoil, to fester, to decompose, to turn sour (e.g. milk)
2. to corrode, to weather, to crumble
3. to become useless, to blunt, to weaken (from lack of practice)
4. to become depraved, to be degenerate, to be morally...
tbd