[ as-id ]
See synonyms for acid on
  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.

  1. something, as a remark or piece of writing, that is sharp, sour, or ill-natured: His criticism was pure acid.

  2. Slang. LSD1.

  1. 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.: Compare alkaline (def. 4).

  2. sharp or biting to the taste; tasting like vinegar; sour: acid fruits.

  1. sharp, biting, or ill-natured in mood, manner, etc.: an acid remark; an acid wit.

  2. Geology. containing much silica.

  3. 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.: Compare basic (def. 3).

Idioms about acid

  1. put on the acid, Australian Slang. to importune someone, as for money, sexual favors, or confidential information.

Origin of acid

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

synonym study For acid

7. 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.

Other words for acid

Other words from acid

  • ac·id·ly, adverb
  • ac·id·ness, noun
  • non·ac·id, noun, adjective
  • pre·ac·id, adjective
  • pre·ac·id·ness, noun
  • sem·i·ac·id, adjective

Words that may be confused with acid Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use acid in a sentence

British Dictionary definitions for acid


/ (ˈæsɪd) /

  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

  1. a slang name for LSD

  1. chem

    • of, derived from, or containing acid: an acid radical

    • being or having the properties of an acid: sodium bicarbonate is an acid salt

  2. sharp or sour in taste

  1. cutting, sharp, or hurtful in speech, manner, etc; vitriolic; caustic

  2. (of rain, snow, etc) containing pollutant acids in solution

  3. (of igneous rocks) having a silica content of more than 60% of the total and containing at least one tenth quartz

  4. metallurgy of or made by a process in which the furnace or converter is lined with an acid material: acid steel

Origin of acid

C17: (first used by Francis Bacon): from French acide or Latin acidus, from acēre to be sour or sharp

Derived forms of acid

  • acidly, adverb
  • acidness, noun
  • acidy, adjective

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for acid


[ ăsĭd ]

  1. Any of a class of compounds that form hydrogen ions when dissolved in water, and whose aqueous solutions react with bases and certain metals to form salts. Acids turn blue litmus paper red and have a pH of less than 7. Their aqueous solutions have a sour taste. Compare base.

Other words from acid

  • acidic adjective

The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Cultural definitions for acid


A sour-tasting material (usually in a solution) that dissolves metals and other materials. Technically, a material that produces positive ions in solution. An acid is the opposite of a base and has a pH of 0 to 7. A given amount of an acid added to the same amount of a base neutralizes the base, producing water and a salt. Common vinegar, for example, is a weak solution of acetic acid.

Notes for acid

Figuratively, acid applies to anything sour or biting; for example, an “acid wit” is sharp and unpleasant.

The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.