acid

noun

|Updated on: 7 Aug 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

—

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

If doing so makes the box too heavy or if items are too weird-shaped to allow it, then wad up sheets of acid-free packing paper to stuff in the free space.

— matthew jancer, Popular Mechanics, "8 Tips to Help You Move Like a Pro," 11 July 2018
Its acid-yellow light strobed the alley, slapping his shadow on each wall of it, moving its blurry black limbs in sync with his.

— andrew liptak, The Verge, "A transgender girl rises up against alien invaders in Rich Larson’s novel Annex," 8 July 2018
In the painted world, Beaverbrook is stricter and Maugham more acid-tongued than ever.

— meghan cox gurdon, WSJ, "Children’s Books: Meeting the People in the Paintings," 5 July 2018
This new oral delivery features insulin-ionic liquid formation encapsulated in an acid-resistant enteric coating.

— fiza pirani, ajc, "These insulin pills could replace daily injections for diabetics, study says," 28 June 2018
The original documents have been painstakingly preserved, rebound into big books of acid-free sleeves, each containing one of the old pages.

— andrew boyd, NOLA.com, "St. Louis Cemetery No. 1: Is Marie Laveau where they say she is?," 22 May 2018
Catherine, a 26-year-old woman with glasses and an acid-yellow bob dyed to match her denim jacket, stands behind a desk decorated with a row of prototype monster dildos.

— allison p. davis, The Cut, "Are We Ready for Robot Sex?," 13 May 2018
Waterways are now showing signs of recovery, as are the upper layers of soil, although they are still strained by the acid deposits.

— lisa rathke, The Christian Science Monitor, "Pollution regulations decrease acid rain, spur red spruce rebound," 11 July 2018
Taste the soup for salt, sweetness and acid balance.

— San Antonio Express-News, "Recipe: Silky Sweet Corn Soup with Indian Coconut-Cilantro Chutney," 11 July 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

—

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

Whether sending up the New York art world or hanging out with acid heads, Wolfe inevitably presented man as a status-seeking animal, concerned above all about the opinion of one’s peers.

— hillel italie, BostonGlobe.com, "Tom Wolfe, pioneering ‘New Journalist,’ dies at 88," 15 May 2018
Shallots will tolerate all but the most acid soils, but dig the earth deeply because the plants put down 8-inch-long feeder roots.

— the editors of organic life, Good Housekeeping, "How To Grow Onions," 1 Feb. 2018
The overall effect is a film that—flaws and all—marries acid satire and a trippy futurescape where oppression is the norm to an ethos of genuine hope.

— vann r. newkirk ii, The Atlantic, "Sorry to Bother You Is a Dystopian Send-Up of Dystopias," 13 July 2018
Click to Read Story A Surprise Medical Solution: Hypnosis Major hospitals are finding hypnotherapy can help sufferers of digestive conditions like heartburn, acid reflux and irritable bowel syndrome.

— sumathi reddy, WSJ, "From Meditation to Medication: Headspace Has a Prescription Strategy," 25 June 2018
The drugs studied were those commonly taken by adults for high blood pressure, acid reflux, pain, and birth control, among others (the authors were careful to exclude adults who were already taking antidepressant medications).

— ronald s. litman, Philly.com, "Unintended consequences of taking prescription medicines," 20 June 2018
The most common of them are drugs such as hormonal birth control, beta-blockers (used for conditions such as high blood pressure, heart attacks, and migraines), and proton-pump inhibitors (used for acid reflux).

— beth mole, Ars Technica, "Common drugs have depression as a possible side effect—a third of us take them," 15 June 2018
This year, there are over 250, ranging from gypsy punk, cosmic Americana, killer blues, Afrobeat, acid folk, and American space rock.

— kathy shiels tully, BostonGlobe.com, "Find your groove along the streets of Somerville during Porchfest," 4 May 2018
The acid aroma mocked me, eating away at my confidence.

— eric asimov, New York Times, "Making (Bad) Vinegar at Home: A Critic’s Confession," 5 Feb. 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