festering festival feast
fest is in the word festival, and so typically used to broadly describe festivals (bookfest, beerfest, etc.). we have more happy fun words associated with this root: festivities, festoons (decorative garlands), festal (celebratory), fiesta, feast, etc. however, there is one fest word much unlike the other: fester, referring to an increasingly infected, inflamed, pus-filled wound. as a metaphor for emotion, fester may refer to a deep-seated resentment that erupts into hatred or vile anger. what an unpleasant word. how did this happen?
seemingly by accident. the original words for these very different concepts rightly sounded very different. festival and its associated words can be traced back to the Latin festivalis (an adjective referring to a church holiday) and festa (referring to church holidays and feasts). on the other hand, fester came from the Latin fistula, referring to a pipe or ulcer.
Old French is where we get the crossover. they turn festivalis into festival. they also turn festa into feste. then they take the Latin fistula and turn that into... festre, referring to a small sore discharging pus. just one letter off! what were you thinking, Old French speakers???