nu·cle·us 
/ˈnu:klijəs/ noun
plural nu·clei /ˈnu:klijəs/ noun /ˈnu:kliˌaɪ/ also nu·cle·us·es [count] 1 biology : the central part of most cells that contains genetic material and is enclosed in a membrane 2 physics : the central part of an atom that is made up of protons and neutrons 3 : a central or most important part of something — usually + of ▪ players who are the nucleus [=core] of the team
