nu·cle·us (no?o?kl?-?s, nyo?o?-)n. pl. nu·cle·i (-kl?-??) or nu·cle·us·es 1. A central or essential part around which other parts are gathered or grouped; a core: the nucleus of a city.2. Something regarded as a basis for future development and growth; a kernel: a few paintings that formed the nucleus of a great art collection.3. 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.4. Anatomy A group of specialized nerve cells or a localized mass of gray matter in the brain or spinal cord.5. 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.6. Chemistry A group of atoms bound in a structure, such as a benzene ring, that is resistant to alteration in chemical reactions.7. 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.8. Meteorology A particle on which water vapor molecules accumulate in free air to form a droplet or ice crystal.9. Linguistics The part of a syllable having the greatest sonority. In the word middlemost (m?d?l-m?st?) the nuclei of the three syllables are (?), (l), and (?); in the Czech word krk (“neck”), the nucleus is (r).[Latin nuculeus, nucleus, kernel, from nucula, little nut, diminutive of nux, nuc-, nut.]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.nucleus (?nju?kl??s) n, pl -clei (-kl??a?) or -cleuses1. a central or fundamental part or thing around which others are grouped; core2. a centre of growth or development; basis; kernel: the nucleus of an idea. 3. (Biology) 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 cell4. (Anatomy) anatomy any of various groups of nerve cells in the central nervous system5. (Astronomy) 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 tail6. (General Physics) physics the positively charged dense region at the centre of an atom, composed of protons and neutrons, about which electrons orbit7. (Chemistry) chem a fundamental group of atoms in a molecule serving as the base structure for related compounds and remaining unchanged during most chemical reactions: the benzene nucleus. 8. (Botany) botany a. the central point of a starch granuleb. a rare name for nucellus9. (Phonetics & Phonology) phonetics the most sonorous part of a syllable, usually consisting of a vowel or frictionless continuant10. (Logic) logic the largest individual that is a mereological part of every member of a given class[C18: from Latin: kernel, from nux nut]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014nu?cle?us (?nu kli ?s, ?nyu-) n., pl. -cle?i (-kli?a?) -cle?us?es. 1. a central part about which other parts are grouped or gathered; core. 2. a specialized, usu. spherical mass of protoplasm encased in a double membrane and found in eukaryotic cells, directing their growth, metabolism, and reproduction, and containing most of the genetic material. 3. the positively charged mass within an atom, composed of neutrons and protons and possessing most of the mass but occupying only a small fraction of the volume of the atom. 4. a mass of nerve cells in the brain or spinal cord in which nerve fibers form connections. 5. a fundamental arrangement of atoms, as the benzene ring, that may occur in many compounds by substitution of atoms without a change in structure. 6. the condensed portion of the head of a comet. 7. a. the central, most prominent segment in a syllable, consisting of a vowel or vowellike consonant, as the a-sound in cat or the l-sound in bottle. b. the most prominent syllable in an utterance or stress group; tonic syllable. [1695?1705;