nucleus

noun

nu·​cle·​us ˈnü-klē-əs 

ˈnyü-

plural nuclei ˈnü-klē-ˌī 

ˈnyü-

also nucleuses

1

a

: the small bright body in the head of a comet

b

: the small brighter and denser portion of a galaxy (see galaxy sense 1b)

2

: a central point, group, or mass about which gathering, concentration, or accretion takes place: such as

a

: a cellular organelle of eukaryotes that is essential to cell functions (such as reproduction and protein synthesis), is composed of nucleoplasm and a nucleoprotein-rich network from which chromosomes and nucleoli arise, and is enclosed in a definite membrane see cell illustration

b

: a mass of gray matter or group of cell bodies of neurons in the central nervous system

c

: a characteristic and stable complex of atoms or groups in a molecule (see molecule sense 1)

especially : ring

the naphthalene nucleus

d

: the positively charged central portion of an atom that comprises nearly all of the atomic mass and that consists of protons and usually neutrons

3

: the peak of sonority in the utterance of a syllable

4

: a basic or essential part : core

players who are the nucleus of the team

Synonyms

• axis
• base
• capital
• center
• central
• core
• cynosure
• epicenter
• eye
• focus
• ground zero
• heart
• hub
• locus
• mecca
• navel
• nerve center
• nexus
• omphalos
• seat

Examples of nucleus in a Sentence

a college campus that was a nucleus of opposition to the war

the nucleus of the movement's methodology has always been passive resistance

Recent Examples on the Web

Another candidate is active galactic nuclei (AGNs) typically found at the center of galaxies and assumed to contain a supermassive black hole. —Jennifer Ouellette, Ars Technica, 23 Nov. 2023

In 1940 scientists used a particle accelerator at the University of California, Berkeley, to bombard an isotope of uranium (which has 92 protons per atom) with nuclei of deuterium (a proton and a neutron stuck together). —Sarah Scoles, Scientific American, 14 Nov. 2023

This contains the nucleus accumbens—an area associated with motivation and action, including compulsive urges. —Emily Mullin, WIRED, 30 Oct. 2023

Astronomers estimated the comet's nucleus stretches 12.4 miles, or roughly twice the size of Mount Everest. —Emma Colton, Fox News, 28 Oct. 2023

In the summer of 1981, Thurston Moore was tapped to curate a nine-day noise-rock showcase at White Columns, then a trendy nucleus of downtown Manhattan’s underground scene. —Samuel Hyland, Pitchfork, 25 Oct. 2023

Most of the lithium on Earth is an isotope called lithium-7, meaning the nucleus has 3 protons and 4 neutrons. —Erik Klemetti, Discover Magazine, 20 Sep. 2023

When later atomic research found that uranium’s unstable nucleus could be used to make a powerful bomb, the U.S. Army’s Manhattan Project began searching for a reliable source of uranium. —Roger Peet, The New Republic, 30 Aug. 2023

Next, Raslan sought out Casey Halpern, an associate professor of neurosurgery at Penn Medicine who is studying the nucleus accumbens as a DBS target for psychiatric conditions. —Emily Mullin, WIRED, 30 Oct. 2023

See More

Word History

Etymology

New Latin, from Latin, kernel, from nuc-, nux nut — more at nut

First Known Use

1668, in the meaning defined at sense 1a

Phrases Containing nucleus

• polar nucleus
• tube nucleus
• endosperm nucleus
• sperm nucleus
• caudate nucleus
• generative nucleus
• suprachiasmatic nucleus

• polar nucleus
• tube nucleus
• endosperm nucleus
• sperm nucleus
• caudate nucleus
• generative nucleus
• suprachiasmatic nucleus

See More

Kids Definition

nucleus

noun

nu·​cle·​us ˈn(y)ü-klē-əs 

plural nuclei -klē-ˌī  also nucleuses

: a central point, group, or mass of something: as

a

: the small, brighter, and denser part of a galaxy or of the head of a comet

b

: a cell part that is characteristic of all living things with the exception of viruses, bacteria, and blue-green algae, that is necessary for heredity and for making proteins, that contains the chromosomes, and that is enclosed in a nuclear membrane

c

: a mass of gray matter or group of neurons in the central nervous system

d

: the central part of an atom that includes nearly all of the atomic mass and consists of protons and usually neutrons

Etymology

from modern Latin nucleus "the central part of something," from Latin nucleus "kernel," derived from nux "nut"

Medical Definition

nucleus

noun

nu·​cle·​us ˈn(y)ü-klē-əs 

plural nuclei -klē-ˌī  also nucleuses

1

: a cellular organelle of eukaryotes that is essential to cell functions (as reproduction and protein synthesis), is composed of nuclear sap and a nucleoprotein-rich network from which chromosomes and nucleoli arise, and is enclosed in a definite membrane

2

: a mass of gray matter or group of nerve cells in the central nervous system

3

: a characteristic and stable complex of atoms or groups in a molecule

especially : ring sense 2

the naphthalene nucleus

4

: the positively charged central portion of an atom that comprises nearly all of the atomic mass and that consists of protons and neutrons except in hydrogen which consists of one proton only