[n] a part of the cell containing DNA and RNA and responsible for growth and reproduction
[n] any histologically identifiable mass of neural cell bodies in the brain or spinal cord
[n] a small group of indispensable persons or things; "five periodicals make up the core of their publishing program"
[n] the positively charged dense center of an atom
[n] (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