domain

domain — noun

1. A specific area of life, work, or thought where a person, group, or organisation

1.nounB2
Definition

A specific area of life, work, or thought where a person, group, or organisation has authority, responsibility, or influence.

Example

Gabriel's main domain of expertise is artificial intelligence, not graphic design.

collocation: domain of expertise

Serious medical decisions belong firmly within the domain of qualified doctors.

phrase: within the domain of

Common collocations
  • domain of expertise
  • within the domain of
  • personal domain
  • public domain
  • fall within one's domain
Synonyms
  • field

    less formal, more common in everyday use

  • realm

    more abstract or imaginative in tone

  • sphere

    often suggests social or interpersonal scope

  • arena

    implies a competitive or active environment

Grammar Patterns

someone's domain

the domain of something

Usage Note

Frequently used with possessive determiners (my domain, her domain) or in the prepositional phrase 'within the domain of'.

Common Mistakes

I work in this domain' (vague).
I work in the domain of software security.
Specify what kind of domain when referring to a professional field.
This problem is out of my domain' (unnatural).
This problem is outside my area of expertise.
For everyday speech, 'area of expertise' or 'field' is more natural than 'domain'.

2. An organised section of the internet identified by a shared ending in web addres

2.nounB1
Definition

An organised section of the internet identified by a shared ending in web addresses, such as .com, .org, or .tw.

Example

The company bought the domain "ecopack.shop" for its new online store.

collocation: bought the domain

Websites ending in ".org" belong to the domain of non-profit organisations.

Common collocations
  • domain name
  • register a domain
  • domain registration
  • top-level domain
  • domain owner
Synonyms

Grammar Patterns

register + domain

domain + name

Usage Note

Commonly paired with 'register', 'buy', 'own', or 'transfer'. In informal speech, 'domain' is often short for 'domain name'.

Common Mistakes

I created a new domain for my blog.
I registered a new domain name for my blog.
You register or buy a domain; you do not 'create' one.

3. The complete set of numbers or values that can be used as inputs for a particula

3.nounC1
Definition

The complete set of numbers or values that can be used as inputs for a particular mathematical function.

Example

The domain of the square-root function includes only non-negative numbers.

pattern: the domain of + [function]

Indra learned how to find the domain of a logarithmic equation in class.

Common collocations
  • domain of a function
  • domain of definition
  • restricted domain
  • natural domain
  • domain and range
Synonyms
Antonyms
  • range

    the set of output values produced by a function

Grammar Patterns

the domain of + function

Usage Note

Often contrasted with 'range', which refers to the set of output values. A common exam question asks students to identify both the domain and the range of a given function.

Common Mistakes

The range of the function is all positive numbers' (when the speaker means inputs).
The domain of the function is all positive numbers.
Domain = possible inputs; range = possible outputs.

4. A physical territory, such as land or a region, that is governed or owned by a p

4.nounB2
Definition

A physical territory, such as land or a region, that is governed or owned by a particular ruler, state, or authority.

Example

The Roman domain once stretched from Britain all the way to North Africa.

possessive: the Roman domain

The emperor sent soldiers to protect his eastern domain from enemy attacks.

possessive: his eastern domain

Common collocations
  • royal domain
  • imperial domain
  • expand one's domain
  • ancestral domain
  • private domain
Synonyms
  • territory

    more common in modern political and legal contexts

  • realm

    often used for kingdoms or abstract areas

  • dominion

    formal or historical, emphasising ruling power

Grammar Patterns

possessive + domain

the domain of + ruler/state

Usage Note

Frequently appears in historical writing about empires, kingdoms, and colonial territories. Less common in modern political language, where 'territory' or 'jurisdiction' is preferred.

Common Mistakes

This desk is my domain' (when casually claiming a workspace).
This is my corner of the office.
Sense 1 (area of interest) is more natural for casual personal space than this territorial sense.

5. In biology, the largest and most general category used to organise all living th

5.nounC1
Definition

In biology, the largest and most general category used to organise all living things, sitting above kingdoms in the classification hierarchy.

Example

All animals, plants, and fungi belong to the domain called Eukarya.

pattern: belong to the domain + [name]

Scientists divide all life into three domains: Bacteria, Archaea, and Eukarya.

Common collocations
  • three domains of life
  • domain Eukarya
  • domain Bacteria
  • domain Archaea
  • domain-level classification
Synonyms

Grammar Patterns

the + number + domains of life

domain + name

Usage Note

Typically encountered in biology textbooks and scientific writing. The three-domain system (Woese, 1990) replaced the older five-kingdom model. Learners at CEFR B2 or below are more likely to encounter 'kingdom' than 'domain'.

Common Mistakes

Kingdom and domain mean the same thing in biology.
Domain is the broader category that sits above kingdom.
Domain is the highest rank; kingdom is one level below it.

Word family

Synonym discussion

Sense: noun/1

Field, realm, sphere, and territory all overlap with domain but differ in tone and scope. Field is the most neutral and common in everyday contexts, especially for professional specialisation (e.g., 'the field of medicine'). Realm sounds more abstract, grand, or imaginative ('the realm of dreams'), and is rarely used for concrete professions. Sphere often describes social or interpersonal range ('sphere of influence') and implies a bounded circle of activity. Territory is the most concrete, suggesting physical or jurisdictional boundaries ('sales territory'), though it also works metaphorically. Domain sits closest to field in practical use but adds a nuance of ownership or control: saying 'her domain is cybersecurity' implies she owns that area, not just that she works in it.

field ↗realm ↗sphere ↗territory ↗

Common collocations

Nouns

Adverbs

Phrases

  • fall within the domain of
  • outside the domain of
  • extend one's domain

Prepositions

Etymology

LatinFrenchEnglish

The word 'domain' entered English through Old French 'demaine', from Latin 'dominium', meaning 'ownership' or 'property', which itself comes from 'dominus' ('lord' or 'master'). The sense of 'area of knowledge' emerged in the 1600s. The internet meaning dates from the 1980s, when the domain name system was created to organise websites into categories.