English Reference
noun · adjective

acid

n. · adj.
US /ˈæsəd/ UK /ˈæsɪd/ acid UK spelling acids

  1. 01 B1 Intermediate Technical Science

    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.

    Simple

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

    In context

    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.

  2. 02 C1 Advanced SlangInformal

    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.

    Simple

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

    In context

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

    Teacher's tip

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

    LSDhallucinogen
  3. 03 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.

    Simple

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

    In context

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

  4. 04 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.

    Simple

    She made an acid comment about his messy hair.

    In context

    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'.

  5. 05 C1 Advanced Informal Music

    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.

    Simple

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

    In context

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

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 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.

This entry
Origin Latin acidus
Level C1 · Advanced
Frequency Common
Updated