- (countable) (chemistry) An acid is a liquid with a high number of hydrogen ions in it that can burn things.
- If something is acid, it is like an acid, from an acid, or acidic.
- The factories nearby have made the lake more acid.
- If something has an acid taste, it is sour.
- Antonym: sweet
- (figurative) If something said or done to you was acid, it was hurtful.
- Their acid comments are painful.