nucleus

play
noun nu·cle·us \ ˈnü-klē-əs , ˈnyü- \

Definition of nucleus

plural nuclei play \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 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 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

Examples of nucleus in a Sentence

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

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

Recent Examples of nucleus from the Web

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'nucleus.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

Origin and Etymology of nucleus

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

Other Cell Biology Terms


NUCLEUS Defined for English Language Learners

nucleus

play
noun

Definition of nucleus for English Language Learners

  • biology : the central part of most cells that contains genetic material and is enclosed in a membrane

  • physics : the central part of an atom that is made up of protons and neutrons

  • : a central or most important part of something


NUCLEUS Defined for Kids

nucleus

play
noun nu·cle·us \ ˈnü-klē-əs , ˈnyü- \

Definition of nucleus for Students

plural nuclei \-klē-ˌī\
1 :a usually round part of most cells that is enclosed in a double membrane, controls the activities of the cell, and contains the chromosomes
2 :the central part of an atom that comprises nearly all of the atomic mass and that consists of protons and neutrons
3 :a central point, group, or mass
  • Those players are the nucleus of the team.

Medical Dictionary

nucleus

play
noun nu·cle·us \ ˈn(y)ü-klē-əs \

medical Definition of nucleus

plural nuclei play \-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 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

Illustration of nucleus



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