SOUR WINE

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".