'fester' originates from Latin, specifically the word 'fistula,' where 'fistula' meant 'pipe or ulcer.'

'fistula' transformed into the Old French word 'festrir,' and eventually became the modern English word 'fester' through Middle English.

Initially, it meant 'an ulcer or sore,' but over time it evolved into its current meaning of 'to become infected and form pus.'