n., pl., -cle·i (-klē-ī'), or -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 large, membrane-bound, usually spherical protoplasmic structure within a living cell, containing the cell's hereditary material and controlling its metabolism, growth, and reproduction.
- Botany.
- The central kernel of a nut or seed.
- The center of a starch granule.
- 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 and containing almost all of the mass of the atom.
- Chemistry. A group of atoms bound in a structure, such as a benzene ring, that is resistant to alteration in chemical reactions.
- Astronomy.
- The central portion of the head of a comet.
- The central or brightest part of a nebula or 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).
[Latin nuculeus, nucleus, kernel, from nucula, little nut, diminutive of nux, nuc-, nut.]
The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.
