Definition of Nucleus

Noun: nucleus (nuclei) n(y)ook-lee-us

A part of the cell containing DNA and RNA and responsible for growth and reproduction
- cell nucleus, karyon
The positively charged dense centre of an atom
A small group of indispensable persons or things
"five periodicals make up the nucleus of their publishing program";
- core, core group
(astronomy) the centre 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
Any histologically identifiable mass of neural cell bodies in the brain or spinal cord
The central structure of the lens that is surrounded by the cortex
- lens nucleus