<p><strong>Noun</strong></p><ul><li>A central part about which other parts are grouped or gathered; core.</li><li>Example: A few faithful friends formed the nucleus of the club.</li><li><strong>Synonyms</strong>: heart, kernel, center</li><li><strong>Biology</strong>: A specialized, usually spherical mass of protoplasm encased in a double membrane, found in most living eukaryotic cells, directing their growth, metabolism, and reproduction, and functioning in the transmission of genetic characters.</li><li><strong>Physics</strong>: The positively charged mass within an atom, composed of neutrons and protons, possessing most of the mass but occupying only a small fraction of the volume of the atom.</li><li><strong>Anatomy</strong>: A mass of nerve cells in the brain or spinal cord in which nerve fibers form connections. Also called condensation nucleus.</li><li><strong>Meteorology</strong>: A particle upon which condensation of water vapor occurs to form water drops or ice crystals.</li><li><strong>Chemistry</strong>: A fundamental arrangement of atoms, as the benzene ring, that may occur in many compounds by substitution of atoms without a change in structure.</li><li><strong>Astronomy</strong>: The condensed portion of the head of a comet.</li><li><strong>Phonetics</strong>: The central, most prominent segment in a syllable, consisting of a vowel, diphthong, or vowellike consonant, as the a-sound in "cat" or the l-sound in "bottled"; peak. The most prominent syllable in an utterance or stress group; tonic syllable.</li></ul>