nucleus

1 a thing or place that is of greatest importance to an activity or interest a college campus that was a nucleus of opposition to the war Synonyms axis, base, capital, central, core, cynosure, epicenter, eye, focus, ground zero, heart, hub, locus, mecca, navel, nerve center, nexus, center, omphalos, seatRelated Words headquarters; happy hunting ground, hive, hotbed, hot spot, playground, playland; kernel, nub, pith; deep, thick; essence, quintessence, soul; attraction, lodestone (also loadstone), magnet, polestar

2 the central part or aspect of something under consideration the nucleus of the movement's methodology has always been passive resistance Synonyms bottom line, bull's-eye, centerpiece, core, essence, gist, heart, kernel, keynote, meat, meat and potatoes, net, nub, nubbin, crux, pith, pivot, point, root, sumRelated Words course, direction, drift, tenor; body, content, substance; hypothesis, proposition, purport, subject, theme, thesis