definition of
nucleus

[1] #1 nucleus n. [cell nucleus, karyon] a part of the cell containing DNA and RNA and responsible for growth and reproduction. wn

[2] #2 nucleus n. the positively charged dense center of an atom. wn

[3] #3 nucleus n. [core, core group] a small group of indispensable persons or things; "five periodicals make up the core of their publishing program". wn

[4] #4 nucleus 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. wn

[5] #5 nucleus n. any histologically identifiable mass of neural cell bodies in the brain or spinal cord. wn