[noo-klee-uhs, nyoo-]

noun, plural nu·cle·i [noo-klee-ahy, nyoo-] /ˈnu kliˌaɪ, ˈnyu-/, nu·cle·us·es.

Origin of nucleus

1695–1705; < Latin: kernel, syncopated variant of nuculeus, equivalent to nucu(la) little nut (nuc-, stem of nux nut + -ula -ule) + -leus noun suffix
Related formssub·nu·cle·us, noun, plural sub·nu·cle·i, sub·nu·cle·us·es.

Synonyms for nucleus Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for nucleus

Contemporary Examples of nucleus

Historical Examples of nucleus

  • The nucleus is the most important part of the cell, and governs its life.

  • The spores are globose or nearly so, with a large "nucleus" nearly filling the spore.

  • The whole plant is gelatinous, with the exception, occasionally, of the nucleus.

  • Let it be granted, however, that at first a nucleus of twelve hundred slaves is formed.

    On Revenues


  • This collection will doubtless form the nucleus of a larger museum.

    The Last Voyage

    Lady (Annie Allnutt) Brassey

British Dictionary definitions for nucleus


noun plural -clei (-klɪˌaɪ) or -cleuses

a central or fundamental part or thing around which others are grouped; core
a centre of growth or development; basis; kernelthe nucleus of an idea
biology (in the cells of eukaryotes) a large compartment, bounded by a double membrane, that contains the chromosomes and associated molecules and controls the characteristics and growth of the cell
anatomy any of various groups of nerve cells in the central nervous system
astronomy the central portion in the head of a comet, consisting of small solid particles of ice and frozen gases, which vaporize on approaching the sun to form the coma and tail
physics the positively charged dense region at the centre of an atom, composed of protons and neutrons, about which electrons orbit
chem a fundamental group of atoms in a molecule serving as the base structure for related compounds and remaining unchanged during most chemical reactionsthe benzene nucleus
  1. the central point of a starch granule
  2. a rare name for nucellus
phonetics the most sonorous part of a syllable, usually consisting of a vowel or frictionless continuant
logic the largest individual that is a mereological part of every member of a given class

Word Origin for nucleus

C18: from Latin: kernel, from nux nut
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for nucleus

1704, "kernel of a nut," 1708, "head of a comet," from Latin nucleus "kernel," from nucula "little nut," diminutive of nux (genitive nucis) "nut," from PIE *kneu- "nut" (cf. Middle Irish cnu, Welsh cneuen, Middle Breton knoen "nut," Old Norse hnot, Old English hnutu "nut"). General sense of "central part or thing, about which others cluster" is from 1762. Use in reference to cells first recorded 1831. Modern atomic meaning is 1912, first by Ernest Rutherford, though theoretical use for "central point of an atom" is from 1844, in Faraday.

Online Etymology Dictionary, © 2010 Douglas Harper

nucleus in Medicine



n. pl. nu•cle•us•es

A large, membrane-bound, usually spherical protoplasmic structure within a living cell, containing the cell's hereditary material and controlling its metabolism, growth, and reproduction.karyon
A membraneless structure in microorganisms that contains genetic material but does not itself replicate.nucleoid
A group of specialized nerve cells or a localized mass of gray matter in the brain or spinal cord.
The substance around which a urinary or other calculus forms.
The positively charged central region of an atom that is composed of protons and neutrons and that contains almost all of the mass of the atom.
A group of atoms bound in a structure, such as a benzene ring, that is resistant to alteration in chemical reactions.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

nucleus in Science



Plural nuclei (nōōklē-ī′)

The positively charged central region of an atom, composed of one or more protons and (for all atoms except hydrogen) one or more neutrons, containing most of the mass of the atom. The strong force binds the protons and neutrons, also known as nucleons, to each other, overcoming the mutual repulsion of the positively charged protons. In nuclei with many nucleons, however, the forces of repulsion may overcome the strong force, and the nucleus breaks apart in the process of radioactive decay. The protons and neutrons are arranged in the nucleus in energy levels known as shells analogous to those of the electrons orbiting the nucleus. The number of protons in the nucleus determines the atom's atomic number and its position in the Periodic Table. See more at atom.
An organelle in the cytoplasm of eukaryotic cells (all cells except prokaryotes) that contains nearly all the cell's DNA and controls its metabolism, growth, and reproduction. The nucleus is surrounded by a pair of membranes called the nuclear envelope, which can be continuous in places with the membranes of the endoplasmic reticulum. The membranes of the nuclear envelope have interconnected pores that allow the exchange of substances with the cell's cytoplasm. The nuclear DNA is wrapped around proteins (called histones) in strands of chromatin, which exists in a matrix known as nucleoplasm (analogous to the cytoplasm outside the nucleus). Just prior to cell division, the chromatin condenses into individual chromosomes, which contain the cell's hereditary information. The nucleus also contains at least one spherical nucleolus, which mainly contains RNA and proteins and directs the construction of the cell's ribosomes. See more at cell.
  1. The solid central part of a comet, typically several kilometers in diameter and composed of ice, frozen gases, and embedded chunks of rock and dust. It is the permanent part of a comet from which the coma and tail are generated as the comet approaches the Sun. See more at comet.
  2. See galactic nucleus.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

nucleus in Culture


plur. nuclei (nooh-klee-eye)

The small, dense center of the atom. The nucleus is composed of protons and neutrons and has a positive electrical charge.


Nuclear physics deals with the composition and structure of the nucleus.


plur. nuclei

In biology, the central region of the cell, in which DNA is stored. The nucleus usually appears as a dark spot in the interior of the cell. Primitive cells (such as bacteria and blue-green algae) have no nuclei.

The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.