Etymology
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acid (adj.)

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 is from 1775; applied to intense colors from 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."

acid (n.)

1690s, from acid (adj.); originally loosely applied to any substance tasting like vinegar, in modern chemistry gradually given more precise definitions from early 18c. 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."

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Definitions of acid
1
acid (adj.)
harsh or corrosive in tone;
a barrage of acid comments
Synonyms: acerb / acerbic / acrid / bitter / blistering / caustic / sulfurous / sulphurous / virulent / vitriolic
acid (adj.)
being sour to the taste;
Synonyms: acidic / acidulent / acidulous
acid (adj.)
having the characteristics of an acid;
an acid reaction
2
acid (n.)
any of various water-soluble compounds having a sour taste and capable of turning litmus red and reacting with a base to form a salt;
acid (n.)
street name for lysergic acid diethylamide;
Synonyms: back breaker / battery-acid / dose / dot / Elvis / loony toons / Lucy in the sky with diamonds / pane / superman / window pane / Zen
From wordnet.princeton.edu