Nucleus

noun

1. The core, central part of something, around which other elements are assembled.
2. An initial part or version that will receive additions.

   "This collection will form the nucleus of a new library."

3. The massive, positively charged central part of an atom, made up of protons and neutrons.
4. A large membrane-enclosed organelle found in eukaryotic cells which contains genetic material.
5. A ganglion, cluster of many neuronal bodies where synapsing occurs.