English Reference

Word

acid

US/ˈæsəd/

UK/ˈæsɪd/

Definitions

01chemical substance

B1 · Intermediate Countable noun Science Technical

n. a chemical substance that is usually sour and can sometimes burn your skin.

n. a chemical compound that yields hydrogen ions in water, often characterised by a sour taste and the ability to react with bases to form salts.

“The scientist added a few drops of acid to the liquid to see if it would change colour.”

“The laboratory technician carefully measured the concentration of the sulphuric acid before beginning the titration process.”

Usage

In scientific contexts, it is often used as a countable noun to refer to specific types of compounds.

Synonyms

Antonyms

02LSD drug

C1 · Advanced Uncountable noun Slang · Informal

n. a powerful drug that makes people see things that are not there.

n. a slang term for lysergic acid diethylamide (LSD), a potent hallucinogenic drug.

“He claimed that he had a strange experience after taking acid at the festival.”

“The counterculture movement of the 1960s was heavily influenced by the widespread recreational use of acid and other psychedelics.”

Teaching tip

This sense is highly informal and associated with drug culture; learners should use it with caution.

Synonyms

LSDhallucinogen

03sour taste

B2 · Upper Intermediate Cooking

adj. having a sharp or sour taste like a lemon.

adj. having a sharp, biting, or sour taste; acidic in flavour.

“The fruit had a very acid taste that made my mouth pucker.”

“The chef balanced the rich, fatty flavours of the duck with an acid reduction of citrus and vinegar.”

Synonyms

Antonyms

04harsh or unkind

C1 · Advanced Literary

adj. describing a way of speaking that is sharp, unkind, or critical.

adj. characterised by a sharp, biting, or sarcastic tone; sour-tempered.

“She made an acid comment about his messy hair.”

“The critic was famous for his acid wit, often dismantling new plays with a single devastating sentence.”

Usage

Usually placed before the noun it describes, such as 'acid wit' or 'acid tongue'.

Synonyms

Antonyms

05music style

C1 · Advanced Music Informal

adj. a style of music that sounds strange or electronic, often linked to dance culture.

adj. denoting a musical genre characterised by repetitive, psychedelic, or distorted electronic sounds.

“The club was playing loud acid house music all night long.”

“The track features the squelching basslines typical of the acid jazz scene that emerged in the late eighties.”

Synonyms

Collocations

Common phrases and expressions where native English speakers use the word “acid” in context.

Verb

01. dissolve in acid

“The metal sample will slowly dissolve in acid during the experiment.”

verb + prep + noun

02. neutralize the acid

“Antacids work by helping to neutralize the acid in your stomach.”

verb + noun

Adjective

03. corrosive acid

“Handle the corrosive acid with extreme care to avoid chemical burns.”

adj + noun

04. dilute acid

“The procedure requires a small amount of dilute acid to trigger the reaction.”

adj + noun

Noun

05. acid rain

“Acid rain has caused significant damage to the local forest ecosystem.”

noun + noun

06. acid reflux

“Eating late at night can often trigger symptoms of acid reflux.”

noun + noun

07. acid test

“The upcoming election will be the acid test for the new government's policies.”

noun + noun

Real-World Examples

“To address this challenge, the researchers developed a platform based on gallic acid, a naturally occurring antioxidant found in plants, fruits and tea leaves.”
Phys.org 21 Aug 2026
“Thiamethoxam killed all the workers within about seven days, while boric acid killed roughly 90% within about two weeks.”
Phys.org 17 Aug 2026

Etymology

Etymology tree Proto-Indo-European *h₂eḱ-der. Latin aceō Proto-Indo-European *dʰeh₁-der. Latin -idus Latin acidusbor. French acidebor. English acid From French acide, from Latin acidus (“sour, acid”), from aceō (“to be sour”). Doublet of agita.

Etymology adapted from Wiktionary, available under CC BY-SA 4.0.

Word family

Related words

Domains

DatabasesMusic

This entry

Exam level
CambridgeCambridgeCambridge English QualificationsThe exam suite from Cambridge University Press & Assessment, from A1 Movers up to C2 Proficiency. The benchmark names double as CEFR labels.C1 AdvancedIELTSIELTSInternational English Language Testing SystemThe 0–9 band test co-owned by the British Council, IDP, and Cambridge. Used for university entry, work, and migration.7.0–8.0TOEFL iBTTOEFL iBTTest of English as a Foreign Language, Internet-Based TestETS's academic English test, the standard route for US university admissions. Scored 0–120, with a 1–6 scale since 2026.1–6 scale: 5.0–5.595–113TOEICTOEICTest of English for International CommunicationETS's workplace English test, big in Japan and Korea. Listening & Reading scores 10–990 and tops out at C1.945–990
Frequency
Common
Level
C1 · AdvancedOxford
Updated

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