sphere

sphere — noun

1. a shape in three dimensions whose outer surface curves smoothly, with all parts

1.nounB1
Definition

a shape in three dimensions whose outer surface curves smoothly, with all parts sitting equally far from the middle point

Example

Dewi carefully rolled the clay into a perfect sphere for the sculpture class.

collocation: perfect sphere; rolled into a sphere

The Earth is not a perfect sphere, because it is slightly wider at the equator.

topic: Earth as a sphere

Common collocations
  • perfect sphere
  • solid sphere
  • metal sphere
  • sphere of clay
Synonyms
  • ball

    more common in everyday language; less precise for geometry

  • globe

    suggests a hollow model of the Earth or a rounded glass object

Antonyms
  • cube

    a solid with flat square faces, the opposite of round

Usage Note

In geometry, 'sphere' technically refers only to the surface, not the solid inside. In everyday use, however, people use it for the whole round object.

Common Mistakes

A sphere is round like a circle.
A sphere is round like a ball.
A circle is flat (2D); a sphere is a 3D shape.

2. a particular field of knowledge, work, interest, or influence in which someone i

2.nounB2
Definition

a particular field of knowledge, work, interest, or influence in which someone is active or has power

Example

Femi moved into the sphere of public health after working in a rural clinic.

pattern: sphere of [field]

The two countries agreed to respect each other's sphere of influence in the region.

idiom: sphere of influence

Common collocations
  • sphere of influence
  • sphere of activity
  • sphere of responsibility
  • public sphere
  • private sphere
Synonyms
  • domain

    slightly more formal; often used for specialised fields

  • realm

    more literary; suggests a broad, almost imaginary scope

  • field

    more concrete and common; used for academic or professional areas

Grammar Patterns

sphere of + noun

Usage Note

Often paired with 'of': sphere of influence, sphere of activity, sphere of interest. The noun before 'of' names the kind of sphere.

Common Mistakes

She works in the sphere of education field.
She works in the sphere of education.
'sphere' already means 'area', so do not add 'field' after it.

3. the sky imagined as a large round dome above the earth, on which the sun, moon,

3.nounC1
Definition

the sky imagined as a large round dome above the earth, on which the sun, moon, stars, and planets seem to move

Example

Ancient astronomers mapped the stars onto a great celestial sphere surrounding the Earth.

compound: celestial sphere

Christopher spent hours studying the celestial sphere through his telescope on clear nights.

Common collocations
  • celestial sphere
  • imaginary sphere
  • night sky
  • dome of the sky
Synonyms
  • firmament

    biblical or poetic term; rarely used in modern science

  • heavens

    common in everyday speech; suggests the sky as a whole

Usage Note

In modern astronomy, 'celestial sphere' describes an imaginary sphere of any size around the Earth used for mapping star positions. It is NOT a physical object.

Common Mistakes

The celestial sphere is a real giant ball in space.
The celestial sphere is an imaginary dome used for mapping stars.
It is a conceptual model, not a physical object.
Idioms

sphere of influence

idiom

the area or region over which a country, person, or organisation has significant power or control

The smaller nations feared being pulled into the superpower's sphere of influence.

As the company grew, its sphere of influence extended into several neighbouring countries.

sphere — verb

sphere — combining form

Word family

  • spherical
    adjectiveB2
  • spherically
    adverbC1
  • sphericity
    nounC2
  • spheroid
    nounC1
  • hemisphere
    nounB2
  • atmosphere
    nounB1
  • biosphere
    nounB2

Synonym discussion

Sense: noun/2

All four words describe an area of activity or knowledge, but they differ in usage. 'Field' is the most common and neutral choice in everyday and academic contexts, such as 'the field of medicine'. 'Domain' is more formal and often implies a clearly defined or owned area of expertise — 'the domain of constitutional law'. 'Realm' has a literary or imaginative tone, suggesting a broad or even abstract scope, as in 'the realm of fantasy'. 'Territory' can refer to a physical area or a figurative area of responsibility, e.g. 'marketing is not my territory'. In geography, 'sphere of influence' remains the standard term for international relations. For most learners, 'field' is the safest default; reserve 'domain' and 'realm' for formal or descriptive writing.

domain ↗realm ↗field ↗territory ↗

Common collocations

Nouns

Adverbs

  • within the sphere
  • outside the sphere
  • beyond the sphere

Phrases

Prepositions

  • sphere of
  • in the sphere

Etymology

GreekLatinFrenchEnglish

The word 'sphere' entered English through Old French 'espere' and Middle English 'spere', from Latin 'sphaera' meaning 'ball, globe, celestial sphere'. The Latin word was borrowed from Greek 'σφαῖρα' (sphaira), which originally meant 'ball' in both the sporting and geometric sense. The ancient Greeks were the first to develop a mathematical theory of spheres. The figurative meaning (a field of activity or influence) emerged in the 1600s, drawing on the image of a ruler's power radiating outward like a sphere. The combining form '-sphere' for layers around the Earth (atmosphere, biosphere) became productive in the 19th century with the rise of earth sciences.