vinegar

This may be a “no duh” to a lot of people, but I didn’t realize the etymology of vinegar until I looked it up, and it immediately seemed obvious in retrospect: It comes to English in the 1300s from Old French, which put together vin, “wine,” and aigre, “sour.” That aigre is also where we get the word eager, which when it entered English in the 1200s originally meant “strenuous, ardent, fierce, angry” and then underwent a positive transformation in the 1300s. In Latin, vinegar was called vinum acetum, “wine turned sour,” and acetum is also the source of acetic, which is related to the Latin acer, “sharp to the senses, pungent, bitter, eager, fierce,” which is also the source of our word acrid.