n. & adj.
n. 1 Chem. a any of a class of substances that liberate hydrogen ions in water, are usu. sour and corrosive, turn litmus red, and have a pH of less than 7. b any compound or atom donating protons. 2 (in general use) any sour substance. 3 sl. the drug LSD.
adj. 1 sharp-tasting, sour. 2 biting, sharp (an acid wit). 3 Chem. having the essential properties of an acid. 4 Geol. containing much silica. 5 (of a colour) intense, bright. acid drop Brit. a kind of sweet with a sharp taste. acid-head sl. a user of the drug LSD. acid house a kind of synthesized music with a simple repetitive beat, often associated with the taking of hallucinogenic drugs. acid radical one formed by the removal of hydrogen ions from an acid. acid rain acid formed in the atmosphere esp. from industrial waste gases and falling with rain. acid test 1 a severe or conclusive test. 2 a test in which acid is used to test for gold etc. put the acid on Austral. sl. seek to extract a loan or favour etc. from. acidic adj. acidimeter n. acidimetry n. acidly adv. acidness n.
[ F acide or L acidus f. acere be sour ]