fester (v.)

late 14c., of wounds, "to become ulcerous, suppurate," from festre (n.) "a fistula" (c. 1300), or from Old French verb festrir "ulcerate, fester," from festre (n.) "small sore discharging pus." The nouns in Old French and Middle English both are from Latin fistula "pipe, ulcer" (see fistula). Related: Festered; festering; festerment.