[ 'nju:klɪəs ]
■ noun ( plural nuclei -lɪʌɪ )
1》 the central and most important part of an object or group.
2》 Physics the positively charged central core of an atom, containing nearly all its mass.
3》 Biology a structure present in most cells, containing the genetic material.
4》 a discrete mass of grey matter in the central nervous system.
Origin
C18: from L., lit. 'kernel, inner part', dimin. of nux , nuc- 'nut'.