English Reference
verb

classify

v.
US /ˈkɫæsəˌfaɪ/ UK /klˈæsɪfˌaɪ/ clas·si·fy UK spelling classifies, classifying

  1. 01 B2 Upper Intermediate

    to put things into groups because they share the same qualities or features.

    to arrange or assign things to groups or categories according to shared qualities or characteristics.

    Simple

    Biologists classify animals into different groups based on their physical features.

    In context

    The library system is designed to classify books by subject matter, making it easier for researchers to locate specific academic texts.

  2. 02 C1 Advanced FormalTechnical Law

    to officially decide that a document or information must be kept secret by the government.

    to designate information or documents as officially secret and accessible only to authorized people.

    Simple

    The government decided to classify the report to protect national security.

    In context

    The intelligence agency chose to classify the documents for fifty years, citing the need to protect active field agents.

    Usage

    Often used in the passive voice: 'the documents were classified'.

    declassify

To understand what makes hot subdwarfs so unusual, one has to picture the standard map astronomers use to classify stars, a diagram where temperature runs along one axis and brightness along the other.

Phys.org· 3 Sept 2026

The European Chemicals Agency classifies the chemical as harmful to aquatic life.

ScienceDaily· 9 Jun 2026

From French classifier. By surface analysis, class + -ify.

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

This entry
Level B2 · Upper Intermediate
Frequency Frequent
Updated