(1)   A part of the cell containing DNA and RNA and responsible for growth and reproduction
(2)   Any histologically identifiable mass of neural cell bodies in the brain or spinal cord
(3)   A small group of indispensable persons or things
"Five periodicals make up the core of their publishing program"
(4)   The positively charged dense center of an atom
(5)   (astronomy) the center of the head of a comet; consists of small solid particles of ice and frozen gas that vaporizes on approaching the sun to form the coma and tail


From , a diminutive of .


  1. The core, central part (of something), round which others 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 organelle found in cells which contains genetic material.
  5. A ganglion, cluster of many neuronal bodies where synapsing occurs.