Word
nucleus
Phoneticsnu·cle·us, stress on the first syllable
US/ˈnukɫiəs/
UK/njˈuːklɪəs/
Definitions
01biology
B2 · Upper Intermediate Countable noun Science Technical
n. the central part of a living cell that contains its genetic information and controls its growth.
n. a membrane-bound organelle within eukaryotic cells containing the genetic material and governing cellular activity.
“The biology teacher showed us how the nucleus holds the DNA of the cell.”
“Under the microscope, the nucleus appeared as a dense, dark-stained sphere, clearly separated from the surrounding cytoplasm by its own membrane.”
Usage
The plural form is 'nuclei'.
02physics/chemistry
B2 · Upper Intermediate Countable noun Science Technical
n. the small, heavy center of an atom that contains protons and neutrons.
n. the positively charged central core of an atom, consisting of protons and neutrons and containing nearly all its mass.
“Energy is released when the nucleus of a heavy atom is split.”
“The stability of an isotope depends largely on the ratio of neutrons to protons within its nucleus.”
Usage
The plural form is 'nuclei'.
Synonyms
03the core of a group
C1 · Advanced Countable noun Formal
n. the small, central group of people or things that a larger group grows around.
n. the central or essential part around which other parts are gathered or a group is formed.
“A small nucleus of dedicated volunteers started the charity ten years ago.”
“The original research team formed the nucleus of the new department, providing the expertise necessary to attract further funding.”
Teaching tip
In this figurative sense, it describes the 'seed' or 'starting point' of a larger organization.
04linguistics
C2 · Proficiency Countable noun Technical
n. the central part of a syllable, which is usually a vowel sound.
n. the central part of a syllable, typically consisting of a vowel or a syllabic consonant.
“In the word 'cat', the vowel 'a' is the nucleus of the syllable.”
“Phonologists distinguish between the onset of a syllable and its rhyme, the latter of which is composed of the nucleus and an optional coda.”
Synonyms
Real-World Examples
“It makes messages, copying and carrying instructions from the cell nucleus to make proteins.” “Instead of studying zinc-70 directly, they examined the beta decay of two separate states of its parent nucleus, copper-70.” Etymology
Learned borrowing from Latin nucleus (“kernel, core”). The earliest uses refer to the head of a comet and the kernel of a seed, both recorded in Lexicon Technicum in 1704. The sense in atomic physics was coined by British scientist Michael Faraday in 1844 in a theoretical meaning.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.
Word family
NOUN
ADJECTIVE
Related words
Domains
- Exam level
- CambridgeCambridgeCambridge English QualificationsThe exam suite from Cambridge University Press & Assessment, from A1 Movers up to C2 Proficiency. The benchmark names double as CEFR labels.B2 FirstIELTSIELTSInternational English Language Testing SystemThe 0–9 band test co-owned by the British Council, IDP, and Cambridge. Used for university entry, work, and migration.5.5–6.5TOEFL iBTTOEFL iBTTest of English as a Foreign Language, Internet-Based TestETS's academic English test, the standard route for US university admissions. Scored 0–120, with a 1–6 scale since 2026.1–6 scale: 4.0–4.572–94TOEICTOEICTest of English for International CommunicationETS's workplace English test, big in Japan and Korea. Listening & Reading scores 10–990 and tops out at C1.785–944
- Frequency
- Frequent
- Level
- B2 · Upper Intermediate
- Updated
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