nucleus[no̵̅o̅′klē əs, nyo̵̅o̅′-]
- The nucleus is the center core of an atom that has a positive charge and that contains most of the atom's mass, or the central heart of an organization or group.
- An example of a nucleus is the center core of an atom.
- An example of a nucleus is the fiction department of a book publisher where most of the money is made and which is considered the heart of the publisher's organization.
A model of an atom showing the nucleus.
nounpl. nuclei or nucleuses
- a thing or part forming the center around which other things or parts are grouped or collected; core
- anything serving as a center of growth or development: the nucleus of a library
- Anat. a group of nerve cells in the brain or spinal column
- Astron. the bright central part of the head of a comet
- Biol. the central, usually spherical or oval mass of protoplasm present in most plant and animal cells, containing most of the hereditary material and necessary to such functions as growth, reproduction, etc.
- Bot. the central point in a starch grain
- Chem., Physics the central part of an atom, the fundamental particles of which are the proton and neutron, except for hydrogen, which is usually composed of one proton only: it carries a positive charge and constitutes almost all of the mass of the atom
- Phonet. the most sonorous portion of a syllable, usually a vowel
- Organic Chem. a fundamental, stable arrangement of atoms that may occur in many compounds by atomic substitution without structural change, as the benzene ring
Origin of nucleusModern Latin ; from Classical Latin a nut, kernel, for nuculeus, diminutive ; from nux (gen. nucis), nut
nounpl. nu·cle·i or nu·cle·us·es
- A central or essential part around which other parts are gathered or grouped; a core: the nucleus of a city.
- Something regarded as a basis for future development and growth; a kernel: a few paintings that formed the nucleus of a great art collection.
- Biology A membrane-bound organelle within a eukaryotic cell that contains most of the cell's genetic material. DNA transcription takes place in the nucleus.
- Anatomy A group of specialized nerve cells or a localized mass of gray matter in the brain or spinal cord.
- Physics The positively charged central region of an atom, composed of protons and neutrons, about which negatively charged electrons orbit. Extremely small and dense, the nucleus contains almost all of the mass of an atom.
- Chemistry A group of atoms bound in a structure, such as a benzene ring, that is resistant to alteration in chemical reactions.
- Astronomy a. The central, often brightest part of the head of a comet.b. The solid part of a comet, composed of ice and smaller amounts of dust and rock.c. The central, often brightest part of a galaxy.
- Meteorology A particle on which water vapor molecules accumulate in free air to form a droplet or ice crystal.
- Linguistics The part of a syllable having the greatest sonority. In the word middlemost (mĭd′l-mōst′) the nuclei of the three syllables are (ĭ), (l), and (ō); in the Czech word krk (“neck”), the nucleus is (r).
Origin of nucleusLatin nuculeus, nucleus, kernel, from nucula, little nut, diminutive of nux, nuc-, nut.
(plural nuclei or nucleuses)
- The core, central part (of something), round which others are assembled.
- An initial part or version that will receive additions.
- This collection will form the nucleus of a new library.
- (chemistry, physics) The massive, positively charged central part of an atom, made up of protons and neutrons.
- (cytology) A large organelle found in cells which contains genetic material.
- (neuroanatomy) A ganglion, cluster of many neuronal bodies where synapsing occurs.
- (linguistics) The central part of a syllable, most commonly a vowel.
From Latin nucleus (“kernel, core"), a diminutive of nux (“nut").