nucleus

definition: 
The central and most important part of an object, movement, or group, forming the basis for its activity and growth
sentence: 
If this proposal is accepted, the government together with the St Lucian organizations could have an extension of the mission in Brooklyn and an important nucleus for the St Lucian community. (Physics) The positively charged central core of an atom, consisting of protons and neutrons and containing nearly all its mass: Electrons produce a small magnetic field as they spin and orbit the nucleus of an atom
difficulty: 
medium
toefl frequency: 
1
toefl classification: