acid

Etymology

From French acide, from Latin acidus (“sour, acid”), from aceō (“I am sour”). Doublet of agita.

adj

1. Sour, sharp, or biting to the taste; tart; having the taste of vinegar.
   acid fruits or liquors
2. (figurative) Sour-tempered.
   His voice was as stern and his face as acid as ever. 1864, Anthony Trollope, The Small House at Allington, 2nd edition, volume 2, Smith, Elder & Co., page 235
3. Of or pertaining to an acid; acidic.
   Like other nyssas, it is in nature a creature of swampy places and looks loveliest where massed close to water and reflected in it, but justifies itself elsewhere if the soil is moist and acid, succeeding in wet clay. 1975, Peter N. Barber, Cecil Ernest Lucas Phillips, The Trees Around Us, page 101
4. (music) Denoting a musical genre that is a distortion (as if hallucinogenic) of an existing genre, as in acid house, acid jazz, acid rock.

noun

1. A sour substance.
2. (chemistry)
   1. Any compound which yields H+ ions (protons) when dissolved in water; an Arrhenius acid.
   2. Any compound that easily donates protons to a base; a Brønsted acid.
   3. Any compound that can accept a pair of electrons to form a covalent bond; a Lewis acid.
3. Any corrosive substance.
   You are in error. / This is terror. / This is your banishment. This land is mine. / This is what you earn. / This is the Law of No Return. / This is the sour dough, this the sweet wine. / This is my history, this my race / And this unhappy man threw acid in my face. 2006, James Fenton, Jerusalem
4. (uncountable, slang) LSD, lysergic acid diethylamide.
   In the end, though, there is one sure way to distinguish a real hippie from his assorted sympathizers: hippies drop acid. That is, real hippies frequently, if irregularly, ingest LSD. 1967, Joe David Brown, editor, The Hippies, New York: Time, Inc, page 171