fester

(fĕsˈtər)

1. To generate pus; suppurate.
2. To form an ulcer.
3. To undergo decay; rot.
4. a. To be or become an increasing source of irritation or poisoning; rankle: bitterness that festered and grew.
   b. To be subject to or exist in a condition of decline: allowed the once beautiful park to fester.