1620s, "of the taste of vinegar," from French acide (16c.) or directly from Latin acidus "sour, sharp, tart" (also figurative, "disagreeable," etc.), adjective of state from acere "to be sour, be sharp" (from PIE root *ak- "be sharp, rise (out) to a point, pierce").

Figurative use in English ("sour, sharp, biting") is from 1775; the word was applied to intense colors by 1916; an acid dye (1888) involves an acid bath. Acid rain "highly acidity in rain caused by atmospheric pollution" is recorded by 1859 in reference to England. Acid drop as a kind of hard sugar candy flavored with tartaric acid is by 1835, with drop (n.) in the "lozenge" sense.

Acid test is American English, 1881, in literal use a quick way to distinguish gold from similar metals by application of nitric acid. Fowler wrote (1920) that it was then in vogue in the figurative sense and "became familiar through a conspicuous use of it during the war by President Wilson."

1690s, from acid (adj.); originally loosely applied to any substance having a sour taste like vinegar, in modern chemistry it was gradually given more precise definitions from early 18c. and is given to many compounds which do not have such a taste.

The slang meaning "LSD-25" first recorded 1966 (see LSD).

When I was on acid I would see things that looked like beams of light, and I would hear things that sounded an awful lot like car horns. [Mitch Hedberg, 1968-2005, U.S. stand-up comic]

Acid rock (type performed or received by people using LSD) is also from 1966; acid house dance music style is 1988, probably from acid in the hallucinogenic sense + house "dance club DJ music style."

"make acid; become acid; render sour," literally or figuratively, 1784 (implied in acidifying); see acid (adj.) + -ify. Related: Acidified.

"containing a large amount of the acid element," 1877, originally in geology; see acid (n.) + -ic. The geological use was chemical, in reference to the acid element (silicon, etc.) in certain salts, and was opposed to basic.

salt of glutamic acid, 1876, from glutamic acid (see gluten) + -ate (3).

"of, pertaining to, or derived from nitre," 1794, originally in reference to acid obtained initially from distillation of saltpeter; see nitre + -ic. Perhaps immediately from French nitrique. The acid was known as aqua fortis, later acid spirit of nitre, then nitric acid (1787) under the system ordered by Lavoisier.

1931, in deoxyribonucleic acid (originally desoxyribonucleic), a nucleic acid which yields deoxyribose on hydrolysis, from deoxyribose (q.v.) + nucleic acid (see nucleic). It is generally found in chromosomes of higher organisms and stores genetic information.

1920, used of milk fermented by acidophilic bacteria, from acidophil (1900), indicating "easily stained by acid dyes," a hybrid word, from Latin acidus "acidic, sour, tart" (see acid (adj.)) + Greek philos "loving" (see -phile); the bacteria so called because they stain easily with an acid dye.

"compound formed by the union of carbonic acid with a base," 1794, from French carbonate "salt of carbonic acid" (Lavoisier), from Modern Latin carbonatem "a carbonated (substance)," from Latin carbo (see carbon).

"quality of being acid or sour; tartness," 1610s, from French acidité (16c.) or directly from Latin aciditatem (nominative aciditas) "sourness," noun of quality from Latin acidus "sour, tart" (see acid (adj.)).