nucleus

nucleus — noun

1. The tiny, positively charged core that sits at the centre of every atom, contain

1.nounB2
Definition

The tiny, positively charged core that sits at the centre of every atom, containing closely packed protons and uncharged neutrons that together make up the bulk of the atom's weight.

Example

Tamar's physics project explained how protons and neutrons are packed inside an atom's nucleus.

collocation: packed inside the nucleus

Splitting the nucleus of a uranium atom releases a huge amount of energy.

grammar pattern: split the nucleus of + noun

Common collocations
  • atomic nucleus
  • split the nucleus
  • nucleus contains
  • nucleus of an atom
  • dense nucleus
Synonyms
  • core

    Less precise; 'core' can refer to the center of any object, while 'nucleus' is specific to atoms in physics.

Antonyms
  • electron cloud

    The region around the nucleus where electrons are found.

Grammar Patterns

the nucleus of + noun

Usage Note

Plural form 'nuclei' (pronounced /ˈnjuːkliaɪ/) is common in scientific writing. The adjective 'nuclear' is used in terms such as 'nuclear physics' and 'nuclear energy'.

Common Mistakes

The nucleas of the atom contains protons.
The nucleus of the atom contains protons.
The spelling is 'nucleus' (not 'nucleas'), from Latin; plural is 'nuclei'.

2. The membrane-bound organelle inside eukaryotic cells that holds the genetic mate

2.nounB2
Definition

The membrane-bound organelle inside eukaryotic cells that holds the genetic material and directs the cell's growth, reproduction, and basic functions.

Example

Under the microscope, Jin could clearly see the round shape of the onion cell's nucleus.

possessive: cell's nucleus

The nucleus of a human cell holds twenty-three pairs of chromosomes made of DNA.

grammar pattern: the nucleus of + noun (biology)

Common collocations
  • cell nucleus
  • nucleus contains DNA
  • nucleus divides
  • nucleus of a cell
  • nucleus membrane
Synonyms
  • cell nucleus

    Full term used when the context of 'nucleus' alone might be ambiguous between atom and cell.

Antonyms
  • cytoplasm

    The material outside the nucleus but inside the cell membrane.

Grammar Patterns

the nucleus of + noun

Usage Note

In biology, the plural 'nuclei' (/ˈnjuːkliaɪ/) is standard. Eukaryotic cells have a true nucleus enclosed by a membrane; prokaryotic cells such as bacteria do not.

Common Mistakes

All cells have a nucleus.
Eukaryotic cells have a nucleus, but bacteria cells do not.
Only eukaryotic cells have a membrane-bound nucleus; prokaryotes have their DNA loose in the cytoplasm.

3. The most important people or elements within a larger organisation or system, ar

3.nounB1
Definition

The most important people or elements within a larger organisation or system, around which all other parts gather or develop.

Example

A small nucleus of parents kept the school sports programme running for over a decade.

collocation: a small nucleus of + people

The old market square became the nucleus around which the modern city centre grew.

grammar pattern: the nucleus around which

Common collocations
  • small nucleus
  • nucleus of supporters
  • nucleus of an idea
  • creative nucleus
  • nucleus around which
Synonyms
  • core

    Nearly interchangeable; 'core' is slightly more common in everyday language, while 'nucleus' has a more formal or organized feel.

  • heart

    More emotional and less structured; 'the heart of the community' emphasises warmth, while 'nucleus' suggests a functional centre.

  • hub

    Emphasises activity and connection (e.g. a transport hub); 'nucleus' focuses more on essential membership.

Antonyms
  • periphery

    The outer edge or less important parts of a group or system.

  • fringe

    The outermost, least central members of an organization.

Grammar Patterns

a nucleus of + noun (group/people/things)

the nucleus of + noun

Usage Note

Typically followed by 'of' to specify the larger entity. Common in business, politics, and community contexts. Unlike the scientific senses, this figurative sense describes an abstract or social centre rather than a physical one.

Common Mistakes

She is the nucleus of the team.
She is part of the nucleus of the team.
'Nucleus' usually refers to a group, not an individual, though in informal usage a single key person may be called 'the nucleus'.

4. The solid, icy central body of a comet, made up of frozen gases, dust, and rock,

4.nounC1
Definition

The solid, icy central body of a comet, made up of frozen gases, dust, and rock, which heats up and releases gas and dust when it approaches the Sun.

Example

The spacecraft sent back clear images of the comet's dark, potato-shaped nucleus.

possessive: comet's nucleus

Near the Sun, the comet's nucleus released gas and dust, forming a glowing coma.

collocation: nucleus releases gas and dust

Common collocations
  • comet's nucleus
  • nucleus of a comet
  • icy nucleus
  • nucleus releases gas
  • solid nucleus

Grammar Patterns

the nucleus of a comet

Usage Note

A specialised astronomy term. The plural 'nuclei' is used when referring to multiple comets. The nucleus is distinct from the coma (the cloud of gas around it) and the tail.

Common Mistakes

The comet's nucleus is the bright tail we see from Earth.
The comet's nucleus is the small solid body at the centre; the tail is what we actually see.
The nucleus itself is too small to see from Earth; we see the coma and tail lit by the Sun.

Word family

  • nuclear
    adjectiveB2
  • nucleate
    verbC1
  • nucleation
    nounC1
  • nucleolus
    nounC2
  • nucleic
    adjectiveC1

Synonym discussion

Sense: noun/3

All four words describe the most important or central part of something, but they differ in nuance. 'Core' is the closest synonym to 'nucleus' and works in most contexts — 'the core of the problem' or 'the core team' — but feels less structured and scientific. 'Heart' adds emotional warmth: 'the heart of the community' suggests care and belonging, whereas 'nucleus' implies function and organization. 'Hub' emphasises activity and connections — a transport hub or a business hub is where things come together and move outward. 'Centre' is the broadest term, covering physical locations ('town centre') and abstract ideas ('centre of attention'), but it lacks the sense of a tightly-knit essential group that 'nucleus' carries. For example, you could say 'a small nucleus of dedicated volunteers kept the library open,' but 'a small heart of volunteers' would sound odd. Use 'nucleus' when you want to suggest a small, indispensable group that other elements depend on.

core ↗heart ↗hubcentre ↗

Common collocations

Nouns

Phrases

  • form the nucleus of
  • act as the nucleus of
  • become the nucleus of

Prepositions

  • nucleus of
  • nucleus around which

Etymology

LatinEnglish

The word 'nucleus' comes directly from Latin, where it meant 'kernel' or 'inner part of a nut' — from 'nux' (nut). In the 17th century, scientists began using it for the central part of a cell, and later for the core of an atom (19th century) and the centre of a comet (20th century). The figurative sense, referring to a small central group of people or things, developed in the 18th century and is now common in business and social contexts. The plural 'nuclei' preserves the Latin inflection.