[ as-id ]
/ ˈæs ɪd /
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Idioms about acid

    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.



acerbic, acid , acrid
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023


What does acid mean?

In science, an acid is a sour-tasting substance that releases hydrogen ions when added to water. Acids will turn litmus to a red color and have a pH lower than 7.

An acid is any substance that will release hydrogen ions when mixed with water. The amount of hydrogen ions that a substance releases is measured on the pH scale, which ranges from 0 to 14. The lower the pH number is, the more hydrogen ions that are being released. Water has a pH of 7, which is neutral on the pH scale. All acids have a pH lower than 7. A pH greater than 7 indicates an alkali, or base.

Acids also have a sour taste, such as the acid found in lemons. A final quality that all acids share is that when they come into contact with litmus paper, they will turn the paper red.

Acids are all around us and are used for a wide variety of purposes. Some common acids you can find in your house include lactic acid (in milk), ascorbic acid (in citrus fruits), and acetic acid (in vinegar).

Why is acid important?

The first records of the term acid come from around 1620. It comes from the Latin word acidus meaning “sour.” Acids have a sour taste, although sometimes it is a very bad idea to put an acid in your mouth.

Several types of acids, such as the ones present in foods we commonly eat, are not only safe to eat but your body actually needs them to stay healthy. Some acids, however, are dangerous and can damage your skin if it touches it or organs if ingested. Hydrochloric acid, which is used in manufacturing, and sulfuric acid, which is used in making fertilizers, are two acids that can burn your skin, damage your organs, and lead to serious health problems with prolonged exposure. Substances like these are considered to be hazardous materials, and there are usually strict laws about handling and transporting these dangerous acids.

Did you know … ?

Your stomach uses a substance called gastric acid to digest the food you eat. It’s also able to kill many bacteria and other organisms that might be in your food or that enter your stomach. Some diseases, spicy foods, or even stress can cause your stomach acid to enter your esophagus. This condition is known as acid reflux. This is why medicines that treat acid reflux by neutralizing stomach acid are referred to as antacids.

What are real-life examples of acid?

Students of chemistry learn about acids early in their studies.


What other words are related to acid?

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True or False?

Acids have a pH higher than 7.

How to use acid in a sentence

British Dictionary definitions for acid

/ (ˈæsɪd) /


Derived forms of acid

acidly, adverbacidness, nounacidy, adjective

Word Origin for acid

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

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.