kernel

[1]	meat , grain , seed , pip , stone , nut , meat , (US) nut-meat
[2]	centre , core , nucleus , heart , essence , quintessence , substance , gist , pith , nub , quiddity
[3]	substance , core , center , centre , essence , gist , heart , heart and soul , inwardness , marrow , meat , nub , pith , sum , nitty-gritty