noun

the intrinsic nature or indispensable quality of something, especially something abstract, which determines its character.

conflict is the essence of drama

quintessence,soul,spirit,ethos,nature,life,lifeblood,core,heart,centre,crux,nub,nucleus,kernel,marrow,meat,pith,gist,substance,principle,central part,fundamental quality,basic quality,essential part,intrinsic nature,sum and substance,reality,actuality,quiddity,esse,nitty-gritty