acid

noun

|Updated on: 12 Jun 2018

Definition of acid

1 : a sour substance; specifically : any of various typically water-soluble and sour compounds that in solution are capable of reacting with a base (see ¹base 7a) to form a salt, redden litmus, and have a pH less than 7, that are hydrogen-containing molecules or ions able to give up a proton to a base, or that are substances able to accept an unshared pair of electrons from a base

2 : something incisive, biting, or sarcastic

a social satire dripping with acid

3 : lsd

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acidy

\ˈa-sə-dē\ adjective

See acid defined for English-language learners

Examples of acid in a Sentence

the acids in your stomach
the kinds of acid found in your stomach

Recent Examples of acid from the Web

This month, Kilauea has been generating steam, volcanic gas, ash clouds and lava, some of which is flowing into the Pacific Ocean and setting off a chemical reaction that produces clouds of acid and fine glass.

— mike ives, New York Times, "Kilauea Volcano’s Lava Fields Offer Scientists a Portal to Mars," 28 May 2018
With its tea-length skirt and old school vibe, the suit was demure, though the shades of acid yellow and chartreuse woven into slate grey kept things exciting.

— janelle okwodu, Vogue, "Of Course Lady Gaga Wore 3 Runway Looks in 24 Hours," 25 May 2018
Contamination The controversy focuses on a large class of chemicals that are variations of perfluorooctanoic acid.

— john timmer, Ars Technica, "EPA boots reporters from meeting on chemicals called a PR disaster," 22 May 2018
The official cause was diabetic ketoacidosis, an insulin deficiency that forces the body to burn fat and produces an overwhelming supply of harmful acid in the blood.

— jeremy olson, chicagotribune.com, "Son's death pushes Minnesota mom into fight against high, rising drug prices," 17 May 2018
Also promised was a tomato smear which was seemingly absent on my compilation and would have rounded out the flavors of the dish as an element of acid was needed to cut through the richness of the thick cut bacon and creamy avocado.

— lindsey mcclave, The Courier-Journal, "You won't regret indulging at downtown Louisville's Atlantic No. 5," 9 May 2018
The good news is that a few injections of hyaluronic-acid filler like Juvederm or Restylane Silk can help rebuild the ear's structure and plump up the lobe area.

— kelsey castañon, refinery29.com, "What It's Really Like To Get Earlobe Fillers For A Stretched Piercing," 2 May 2018
Find a cleanser with hyaluronic acid, like Ernest Supplies’ Gel Cleanser, or swap your daytime moisturizer out at bedtime, in favor of an hyaluronic-acid night cream like Roc Retinol Correxion for Sensitive Skin.

— adam hurly, GQ, "These Are the Old School Grooming Rules You Should Be Breaking," 28 Mar. 2018
The meat is smoky and tender, with a slow-building spice that’s balanced with a bite of acid from the pungent onion sauce.

— mark kurlyandchik, Detroit Free Press, "Best New Restaurant #7: Maty’s African Cuisine, Detroit," 13 Feb. 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'acid.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

Origin and Etymology of acid

borrowed from Medieval Latin acidum, going back to Latin, neuter of acidus ²acid

NEW! Time Traveler

First Known Use: 1650

in the meaning defined at sense 1

See Words from the same year

Other Chemical Engineering Terms

alkali, cation, decant, hygroscopic, isotope, oxidize, slurry, solute, viscous

acid

adjective ac·id \ ˈa-səd \

Definition of acid

1 a : sour, sharp, or biting to the taste

an acid flavor

b : sharp, biting, or sour in manner, disposition, or nature

an acid individual

an acid personality

c : sharply clear, discerning, or pointed

an acid wit

acid criticism

d : piercingly intense and often jarring

acid yellow

2 a : of, relating to, or being an acid; also : having the reactions or characteristics of an acid

acid soil

an acid solution

b of salts and esters : derived by partial exchange of replaceable hydrogen

acid sodium carbonate NaHCO₃

c : containing or involving the use of an acid (as in manufacture)

an acid bath

d : marked by or resulting from an abnormally high concentration of acid

acid indigestion

3 : relating to or made by a process in which the furnace is lined with acidic material and an acidic slag is used

acid steel

4 : rich in silica

acid rocks

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acidly

adverb

—

acidness

noun

See acid defined for English-language learners

See acid defined for kids

Examples of acid in a Sentence

He washes his windows with an acid solution of vinegar and water.
with her acid personality, my aunt could be relied upon to bring some much-needed balance to the holiday gush

Recent Examples of acid from the Web

French’s medical issues included sleep apnea, high blood pressure and acid reflux, family members said.

— katy moeller, idahostatesman, "Family of missing Boise man says sheriff notified them of human bone found in river," 6 June 2018
At Karachi's rally, held amid tight security, hundreds of Muslims and minority Christian women stood up as a sign of respect when the acid attack victim joined them.

— Bloomberg.com, "The Latest: 'Black Panther' Star Speaks At UN Event," 8 Mar. 2018
The prescription drug is used to treat acid reflux and stomach ulcers.

— gwen filosa, miamiherald, "Why did he have cocaine? He said he was protecting the neighborhood kids | Miami Herald," 21 May 2018
Pink hydrangeas need an alkaline soil and blue and acid soil.

— tom maccubbin, OrlandoSentinel.com, "Hydrangeas need special handling," 17 May 2018
Using light signatures, MISE will also scan the moon's surface to map the distribution of organics, salts, acid hydrates, water ice phases, and other materials that can give hints about Europa’s potential ability to support life.

— eric niiler, WIRED, "How NASA Will Look for Geysers (and Life) on Europa," 14 May 2018
Just as older generations of musicians were seduced by the electric guitar, Hopkins, as a boy, was seduced by the Roland TB-303, the synthesizer whose squelchy, serrated sound defined the genre known as acid house.

— ronan farrow, The New Yorker, "An Electronic Soundtrack for Spiritual Awakening," 23 Apr. 2018
Over the years, artists began to use additional techniques to their reperatories, such as laminating, mosaic assemblage, grinding, casting, acid etching, engraving and plating to their repertory.

— george fishman, miamiherald, "This art speaks to the heart. Even when you can see through it. | Miami Herald," 8 May 2018
Already, acid-tongued criticism of Ms. Markle can be found in The Daily Mail.

— ellen barry, New York Times, "Britain’s Wedding-Mad Tabloids Feel a Cold Royal Shoulder," 1 May 2018

Origin and Etymology of acid

borrowed from French & Latin; French acide, going back to Middle French, borrowed from Latin acidus, adjective derivative from the base of acēre "to be sour" — more at acetic acid

NEW! Time Traveler

First Known Use: 1649

in the meaning defined at sense 1a

See Words from the same year

acid Synonyms

Other Chemical Engineering Terms

alkali, cation, decant, hygroscopic, isotope, oxidize, slurry, solute, viscous

ACID Defined for English Language Learners

acid

adjective

Definition of acid for English Language Learners

: of, relating to, or having the qualities of an acid
: sharp, strong, and critical in tone

acid

noun

Definition of acid for English Language Learners

chemistry : a chemical with a sour taste that forms a salt when mixed with a base

ACID Defined for Kids

acid

adjective ac·id \ ˈa-səd \

Definition of acid for Students

1 : having a taste that is sour, bitter, or stinging

2 : harsh or critical in tone

acid remarks

3 : of, relating to, or like an acid

an acid solution

—

acidly

adverb

spoke acidly

acid

noun

Definition of acid for Students

: a chemical compound that tastes sour and forms a water solution which turns blue litmus paper red

Medical Dictionary

acid

adjective ac·id \ ˈas-əd \

medical Definition of acid

1 : sour, sharp, or biting to the taste

2 a : of, relating to, or being an acid; also : having the reactions or characteristics of an acid

an acid solution

b of salts and esters : derived by partial exchange of replaceable hydrogen

acid sodium carbonate NaHCO₃

c : marked by or resulting from an abnormally high concentration of acid

acid indigestion

—not used technically

acid

noun

medical Definition of acid

1 : a sour substance; specifically : any of various typically water-soluble and sour compounds that in solution are capable of reacting with a base to form a salt, that redden litmus, that have a pH less than 7, and that are hydrogen-containing molecules or ions able to give up a proton to a base or are substances able to accept an unshared pair of electrons from a base

2 : lsd