Nucleus

Nucleus fundamentally means "kernel" or "central core." Nucleus was pronounced NEW-klee-us. The plural was nuclei, pronounced NEW-klee-eye. In science, it has many uses:

In biology, the region of a eukaryotic cell 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 in turn contain the cell's DNA.

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

In astronomy, the bright, central part of a 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 is called nuclei; for example, the nucleus caudatus.