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

Electrons are typically seen flitting around their atoms, but a team of physicists has now imaged the particles in a very different state: nestled together in a quantum phase called a Wigner crystal, without a nucleus at their core. —Isaac Schultz / Gizmodo, Quartz, 12 Apr. 2024

As the comet approaches the sun, the ice begins to turn to gas that can burst out of the comet in a cloud of dust that creates a huge, fuzzy cloud around the nucleus called the coma. —Claire Reid, Journal Sentinel, 19 Mar. 2024

The devices have two electrodes that target a pea-size structure deep inside the brain called the subthalamic nucleus. —Brenda Goodman, CNN, 15 Mar. 2024

The additional energy moves the outermost electron into a higher orbit, where the attraction of the nucleus is weakened. —Paul Smith-Goodson, Forbes, 20 Feb. 2024

By smashing atomic nuclei or subatomic particles together at near-light speed, accelerators like LHC have helped dramatically push the boundaries of physics and technology. —IEEE Spectrum, 17 Feb. 2024

Nuclear energy Nuclear energy is produced by nuclear fission, when the nucleus of an atom splits apart into two smaller atoms and releases a boatload of energy. —Kylie Martin, Detroit Free Press, 28 Mar. 2024

The championship nucleus is about to get augmented by a new wave led by Wyatt Langford, Evan Cater, Josh Jung and Jack Leiter. —Danny Emerman, The Mercury News, 24 Mar. 2024

This is important because the inner electrons act as a shield and weaken the attraction between the single outer electron and the atom’s nucleus. —Paul Smith-Goodson, Forbes, 20 Feb. 2024

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

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

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