nu|cle|us

nu|cle|us «NOO klee UHSYOO-», noun, plural -cle|i or -cle|us|es.

1. a central part or thing around which other parts or things are collected: »

A very strange old gentleman, whose eccentricity had become the nucleus for a thousand fantastic stories (Hawthorne). The few hundred families, which formed the original nucleus of her citizenship (Charles Merivale).

SYNONYM(S): center, core, heart.

2. Figurative. a beginning to which additions are to be made: »

His five-dollar bill became the nucleus of a flourishing bank account. He had the nucleus of a good plan, but it required working out.

3. a proton, or a group of protons and neutrons, or other nuclear particles, forming the central part of an atom. A nucleus has a positive charge of electricity. The nucleus forms the core around which the electrons orbit. It also contains most of the mass of the whole atom. »

The exact ratio of protons to neutrons in a stable nucleus depends on the total number of particles it contains (J. Little).

4. the fundamental, stable arrangement of atoms in a particular compound, to which other atoms may be joined in various ways.

5. Biology. a mass of specialized protoplasm found in most plant and animal cells, without which the cell cannot grow and divide. A nucleus is different in structure from the rest of the cell. It consists of complex arrangements of proteins, nucleic acids, and lipids surrounded by a delicate membrane, and typically containing such structures as chromosomes and nucleoli. The nucleus controls growth, cell division, and other activities, and contains DNA, a nucleic acid which passes on the genetic characteristics of the cell. »

The hereditary endowment of a plant or animal is now known to be determined by a very special kind of material found primarily in the threadlike chromosomes that may be seen under the microscope in the nucleus of the cell (Atlantic).

6. the relatively dense, central part of a galaxy or of a comet's head: »

The astronomers tell us that some of these comets have no visible nucleuses (James Fenimore Cooper).

7. one of a number of anatomically distinct masses of gray matter in the brain or spinal cord of vertebrates, consisting of the cell bodies of nerve cells, having special functions, and connected to one another by nerve fibers.

8. Meteorology. a speck of dust or other particle upon which water vapor condenses, as to form a drop; condensation nucleus.

9. the kernel of a seed.

╂[< Latin nucleus kernel (diminutive) < nux, nucis nut]