acid

UK: /ˈæsɪd/ US: /ˈæsɪd/ ,(as′id)

WordReference Random House Learner's Dictionary of American English © 2025

ac•id /ˈæsɪd/   n. 

1. Chemistry a chemical substance capable of turning blue litmus paper red; a substance with a sour taste:
   [uncountable] How much acid is in the soil?
   [countable] An acid will dissolve the grease.
2. Slang Terms [uncountable] the drug LSD.

adj. 

3. Chemistry belonging or relating to acids.
4. sharp or biting to the taste;
   sour:
   the acid flavor of lime.
5. sharp, biting, or sarcastic:
   acid criticism.

a•cid•ic /əˈsɪdɪk/  adj. 
a•cid•i•ty, n. [uncountable]
ac•id•ly, adv. 
ac•id•ness, n. [uncountable] See -acr-.

WordReference Random House Unabridged Dictionary of American English © 2025

ac•id  (as′id), n. 

1. Chemistry a compound usually having a sour taste and capable of neutralizing alkalis and reddening blue litmus paper, containing hydrogen that can be replaced by a metal or an electropositive group to form a salt, or containing an atom that can accept a pair of electrons from a base. Acids are proton donors that yield hydronium ions in water solution, or electron-pair acceptors that combine with electron-pair donors or bases.
2. a substance with a sour taste.
3. something, as a remark or piece of writing, that is sharp, sour, or ill-natured:
   His criticism was pure acid.
4. Slang Terms See LSD (def. 2).
5. British Terms put on the acid, [Australian Slang.] to importune someone, as for money, sexual favors, or confidential information.

adj. 

6. Chemistry
   • belonging or pertaining to acids or the anhydrides of acids.
   • having only a part of the hydrogen of an acid replaced by a metal or its equivalent:
     an acid phosphate.
   • having a pH value of less than 7. Cf. alkaline (def. 4).
7. sharp or biting to the taste;
   tasting like vinegar;
   sour:
   acid fruits.
8. sharp, biting, or ill-natured in mood, manner, etc.:
   an acid remark; an acid wit.
9. Geology containing much silica.
10. Metallurgy noting, pertaining to, or made by a process in which the lining of the furnace, or the slag that is present, functions as an acid in high-temperature reactions in taking electrons from oxide ions: usually a siliceous material, as sand or ganister. Cf. basic (def. 3).

• Latin acidus sour, akin to ācer sharp, acētum vinegar, acescent, acicula
• 1620–30

ac′id•ly, adv. 
ac′id•ness, n. 
Synonyms

• 8. acerbic, stinging, vitriolic, tart.
  Acid, astringent are terms used figuratively of wit or humor.
  Acid suggests a sharp, biting, or ill-natured quality:
  an acid joke about an opponent.
  Astringent connotes severity but usually also a bracing quality, as of something applied with curative intent:
  astringent criticism.

Collins Concise English Dictionary © HarperCollins Publishers::

acid / ˈæsɪd/ noun

1. any substance that dissociates in water to yield a sour corrosive solution containing hydrogen ions, having a pH of less than 7, and turning litmus red
   See also Lewis acid
2. a sour-tasting substance
3. a slang name for LSD

adjective

1. of, derived from, or containing acid
2. being or having the properties of an acid
3. sharp or sour in taste
4. cutting, sharp, or hurtful in speech, manner, etc; vitriolic; caustic

Etymology: 17th Century: (first used by Francis Bacon): from French acide or Latin acidus, from acēre to be sour or sharp

ˈacidly adverb

ˈacidness noun

Collins Concise English Dictionary © HarperCollins Publishers::

Acid House, Acid noun

1. a type of funk-based electronically edited disco music of the late 1980s, which has hypnotic sound effects and is associated with hippy culture and the use of the drug ecstasy

Etymology: 20th Century: perhaps from acid (LSD) + House ( music)