1. adj. Sour, sharp, or biting to the taste; tart; having the taste of vinegar.
acid fruits or liquors
2. adj. (figuratively) Sour-tempered.
3. adj. Of or pertaining to an acid; acidic.
4. adj. (music) Denoting a musical genre that is a distortion (as if hallucinogenic) of an existing genre, as in acid house, acid jazz, acid rock.
5. subst. A sour substance.
6. subst. (chemistry) Any of several classes of compound having the following properties:
7. subst. Any of a class of water-soluble compounds, having sour taste, that turn blue litmus red, and react with some metals to liberate hydrogen, and with base
8. subst. Any compound that easily donates protons; a Brønsted acid
9. subst. Any compound that can accept a pair of electrons to form a covalent bond; a Lewis acid