1. A sour-tasting liquid produced usually by oxidation of the alcohol in wine or cider and used as a condiment or food preservative: Vinegar can be made by certain bacteria operating on sugar-water solutions directly, without intermediary conversion to ethanol.

2. A sour liquid consisting of dilute and impure acetic acid, obtained by acetous fermentation from wine, cider, beer, ale, etc.; used as a condiment, preservative, etc.: Vinegar is a sour-tasting liquid made from the oxidation of ethanol in wine, cider, beer, fermented fruit juice, or nearly any other liquid containing alcohol.
3. In pharmacy, a solution of a medicinal substance in dilute acetic acid: Vinegar, as a diluted acetic acid, is a colorless and pungent liquid used in making pharmaceuticals and plastics.
4. A descriptive term for sour or irritable speech, manner, or countenance: The audience recognized a note of vinegar in the speaker's voice.
5. Informal for vigor; high spirits; vim: The children were full of vinegar and enthusiasm just before taking off for the day trip to the fun park.
6. Etymology: a word that comes from Old French vinaigre, meaning "sour wine"; based on Latin vinum, "wine" + acer, "sour".