Nucleus

Nucleus fundamentally means "kernel" or "central core." Nucleus is pronounced NEW-klee-us. The plural is nuclei, pronounced NEW-klee-eye. In science, this term has five main uses:

Structure of a typical neuron

Cell Nucleus
Dendrite Soma Axon Nucleus Node of Ranvier Axon terminal Schwann cell Myelin sheath

In biology, the region of a eukaryotic cell about 10 - 20 nanometres in diameter which usually looks dark and round under the microscope. It was identified and given the name long before it was discovered that it contains the chromosomes, which contain the cell's DNA.

In physics, the central part of an atom which contains neutrons and protons.

In astronomy, the bright, central part of a galaxy or comet;

In meteorology, the tiny grains of dust which induce water vapor to condense out into raindrops or snowflakes;

In medicine, some parts of the brain are called nuclei; for example, the nucleus caudatus.