nub

[1]	nubble , projection , protuberance , knob , boss , lump , bump , knop , protrusion , bulge , node , knot , excrescence , swelling , tumescence
[2]	essence , stub , core , heart , nucleus , crux , point , gist , pith , kernel , nucleus , meat , (sum and) substance , main issue , gravamen
[3]	kernel , substance , core , center , centre , essence , gist , heart , heart and soul , inwardness , marrow , meat , pith , sum , nitty-gritty