Definition of acid in English:


Syllabification: ac·id
Pronunciation: /ˈasid


  • 1A chemical substance that neutralizes alkalis, dissolves some metals, and turns litmus red; typically, a corrosive or sour-tasting liquid of this kind: rainwater is a very weak acid traces of acid Often contrasted with alkali or base1.
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    • It can withstand high temperatures and is resistant to many corrosive substances such as acids and alkalis.
    • Zinc is a fairly active metal that dissolves in both acids and strong alkalis.
    • Copper is a moderately reactive metal that dissolves in most acids and alkalis.
  • 1.1Bitter or cutting remarks or tone of voice: she was unable to quell the acid in her voice
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    • The bitterness and acid in his voice reassured me Peter was still in there, but he was very, very upset.
    • I guess I hadn't spoken with such acid in my tone for a while.
    • Her tone lacked its previous acid; she almost sounded sincere.
  • 2 Chemistry A molecule or other entity that can donate a proton or accept an electron pair in reactions.
    More example sentences
    • They would like to use their carborane acids to bind protons to atoms of the inert gas xenon.
    • Weak acids have dissociable protons like strong acids, but they simply do not dissociate completely.
    • The acid's active ingredient is positively charged hydrogen, so a transfer of electrons takes place between the zinc and the acid.
  • 3 informal The drug LSD.
    More example sentences
    • He has used mescaline, cocaine and acid, although he has not indulged in intravenous drugs.
    • He looked around more, seeing many different things that he would never expect: cocaine, meth and acid.
    • That heroin and acid were and are illegal didn't seem to stop him.

Acids are compounds that release hydrogen ions (H+) when dissolved in water. Any solution with a pH of less than 7 is acidic, strong acids such as sulfuric or hydrochloric acid having a pH as low as 1 or 2. Most organic acids ( carboxylic or fatty acids) contain the carboxyl group COOH


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  • 1Containing acid or having the properties of an acid; in particular, having a pH of less than 7: poor, acid soils Often contrasted with alkaline or basic.
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    • In the case of acid soils, burning decreases acidity, which starts to increase again during the planting period.
    • Boxwood prefer slightly acid to slightly alkaline soil and do very well when planted in early fall.
    • It used to be that, if you had a very acid soil, the hydrangeas would be bluer; more alkaline soil, your hydrangeas would be pinker.
  • 1.1 Geology (Of rock, especially lava) containing a relatively high proportion of silica.
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    • Acraman occurs in the Gawler Range Volcanics, a Mesoproterozoic continental suite of mainly acid lavas and ash flows.
    • In the Southern Central Iberian Zone there are minor acid volcanic rocks intercalated with Caradoc-Ashgill limestones.
    • These deposits are intimately associated with the porphyric parts of intermediate to acid plutons in orogenic belts.
  • 1.2 Metallurgy Relating to or denoting steelmaking processes involving silica-rich refractories and slags.
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    • In the acid processes, deoxidation can take place in the furnaces, leaving a reasonable time for the inclusions to rise into the slag and so be removed before casting.
    • Therefore, a business opportunity could be created for an entrepreneur interested in running the acid separation and purification process.
    • As it happened, Workington's adherence to acid steelmaking sealed the fate of the ore dock in the next few years.



More example sentences
  • The grilled lemon chicken special was great, and showed that the chef has real skill - there's nothing better than the blend of acidy lemon with a bit of charred poultry.
  • The taste changes to become sweet and a little acidy.
  • There's homemade tzatziki with everything, and it's acidy and flavourful.


early 17th century (in the sense 'sour-tasting'): from Latin acidus, from acere 'be sour'.

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Word of the day coloratura
Pronunciation: ˌkɒlərəˈtjʊərə
elaborate ornamentation of a vocal melody