classify

classify — verb

1. to put people or things into a set of categories so that each one is grouped wit

1.verbtransitiveC1
Definition

to put people or things into a set of categories so that each one is grouped with others that share the same qualities.

Example

Librarians classify each book by topic, such as history, science, or art.

classify + by + topic/category

The hospital classifies patients by how urgent their medical needs are.

Common collocations
  • classify by
  • classify into
  • classify according to
Synonyms
  • categorize

    very similar, but 'categorize' can be looser and less systematic than 'classify'

  • sort

    more about physically arranging or separating by a simple criterion, often less formal

  • group

    simpler and more general; focuses on putting together rather than assigning labels

Antonyms
  • mix

    to combine different types together rather than separating them

  • lump together

    to treat different items as the same group without distinction

Grammar Patterns

classify + object + into + plural noun phrase

classify + object + as + complement

Usage Note

Frequently occurs in scientific, academic, library, and commercial contexts. The object names what is being grouped, followed either by into + the set of categories or by as + the specific label assigned.

Common Mistakes

I classified the books in alphabetical order.
I sorted the books in alphabetical order.
'sort' describes physical arrangement by a simple rule; 'classify' means grouping by type or shared qualities.
Please classify these names from oldest to youngest.
Please rank these names from oldest to youngest.
'rank' arranges items along a scale; 'classify' assigns them to categories that are not ordered by level.

2. to mark government, military, or corporate information as officially secret so t

2.verbtransitiveC1
Definition

to mark government, military, or corporate information as officially secret so that only authorised people may see it.

Example

The government classified the report on the new defence system as top secret.

passive: classified as + secrecy level

Military officials classified the documents about troop movements to protect national security.

Common collocations
  • classify documents
  • classified information
  • classified as secret
Synonyms
  • restrict

    broader; means limiting access without the official secrecy process

  • withhold

    focuses on not releasing information, not on the labelling process

Antonyms
  • declassify

    the direct opposite — to remove official secrecy status from information

  • release

    to make information available, often after declassification

Grammar Patterns

be classified + as + adjective (secret/confidential)

classify + document/information

Usage Note

Commonly appears in the passive voice (the documents were classified). The secrecy level follows as: classified as confidential, classified as restricted. This sense is limited to official or institutional contexts — not used for personal secrets.

Common Mistakes

My sister classified her diary under her bed.
My sister hid her diary under her bed.
'classify' in this sense is only used for official secrecy, not for hiding personal items.
The teacher classified the exam scores.' (when meaning 'graded').
The teacher graded the exam scores.
'classify' does not mean to evaluate or assign marks.

Word family

  • classification
    nounB2
  • classified
    adjectiveB2
  • classifier
    nounC1
  • reclassify
    verbC1
  • unclassified
    adjectiveC1
  • classifiable
    adjectiveC2
  • declassify
    verbC2

Synonym discussion

Sense: verb/1

All four verbs involve arranging items, but they differ in how. Classify and categorize are the closest pair: both mean assigning items to groups based on shared qualities. Classify is more systematic and formal — scientists classify species using a fixed taxonomy, while categorize is looser and can be everyday (categorize expenses for a budget). Sort focuses on physically separating or ordering by a simple criterion (sort mail by postcode); it is less about labels and more about arrangement. Rank arranges items on a scale from high to low by quality, importance, or value (rank students by test scores). You can classify books by genre but rank them by popularity — the two operations answer different questions.

categorize ↗classify ↗sort ↗rank ↗

Common collocations

Nouns

Adverbs

Phrases

  • into categories
  • into groups
  • according to type
  • as confidential
  • as top secret

Prepositions

Etymology

LatinFrenchEnglish

Classify combines the Latin classis ('a division or group of Roman citizens') with the English suffix -fy ('to make or cause'). It first appeared in the late 1700s as a term in natural history, where scientists needed a word for arranging plants and animals into systematic groups based on shared features.