nub
noun.
a small lump or protuberance
Synonym: nubble
noun.
a small piece
a nub of coal|a stub of a pencil
Synonym: stub
noun.
the choicest or most essential or most vital part of some idea or experience
the gist of the prosecutor's argument|the heart and soul of the Republican Party|the nub of the story
Synonym: center, sum, substance, pith, nitty-gritty, meat, marrow, kernel, inwardness, heart and soul, heart, gist, essence, core, centre