1. (

• nucleus ,
• cell_nucleus ,
• karyon

) a part of the cell containing DNA and RNA and responsible for growth and reproduction ;

2. (

• nucleus

) the positively charged dense center of an atom ;

3. (

• core ,
• nucleus ,
• core_group

) a small group of indispensable persons or things; "five periodicals make up the core of their publishing program" ;

4. (

• nucleus ,

) (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 ;

5. (

• nucleus ,

) any histologically identifiable mass of neural cell bodies in the brain or spinal cord ;

6. (

• lens_nucleus ,
• nucleus ,

) the central structure of the lens that is surrounded by the cortex ;