From Old French festre, from Latin fistula
- To become septic; to become rotten.
- To worsen, especially due to lack of attention.
- Deal with the problem immediately; do not let it fester.
- To cause to fester or rankle.
- For which I burnt in inward, swelt'ring hate, / And fester'd rankling malice in my breast.
become septic or rotten
To worsen, especially due to lack of attention