festering

The word 'festering' originates from a medical term for a specific kind of ulcer. Its core, 'fester', entered English via Old French from the Latin fistula, which described a pipe or tube, and by extension, an ulcer that forms a passage. This literal sense of a wound secreting pus evolved metaphorically to describe anything that rots or worsens over time, such as resentment or a social problem. The addition of the present participle suffix '-ing' transforms the verb into an adjective, describing a state of ongoing decay or intensification, whether physical or emotional.

Structure: fester (to rot) + ing (adjective-forming suffix) fester (from Old French festre, meaning 'fistula' or 'abscess', ultimately from Latin fistula, meaning 'pipe' or 'ulcer'); ing (from Old English -ende, present participle suffix, forming adjectives from verbs).