We get our word vinegar from the French word vinaigre, which had the same meaning as today's term. This is actually a portmanteau, that of vin, meaning "wine", and aigre, meaning "sour". It sort of makes sense if you think about vinegar as sour wine; it is fermented, and red wine vinegar is a thing. Vin is from the Latin word vinum, from the Proto-Italic word winom, from the Proto-Indo-European root woyhnom, which still meant "wine". Meanwhile, the word aigre was coming from the Latin word acer, which had several definitions, including "sharp", "bitter", and "sour". This, through Proto-Italic akris, derives from the Proto-Indo-European reconstruction hkros, which also meant "sharp". Now here comes the interesting part: remember aigre, which meant "bitter"? That came into English as a word that had a definition more like "fierce" or "angry", which later evolved into our word eager, which developed under a correlation of "powerful emotions".
Adam Aleksic, a freshman studying linguistics at Harvard University, has been described as the internet's sixth most famous etymologist. He has disturbing interests in words, vexillology, geography, board games, limericks, and law, and he loves writing about himself in the third person.
The Etymology Nerd