nub

(noun) a small lump or protuberance. Synonyms: nubble.

(noun) a small piece. Synonyms: stub. Examples: "A nub of coal." "A stub of a pencil."

(noun) the choicest or most essential or most vital part of some idea or experience. Synonyms: kernel, substance, core, center, centre, essence, gist, heart, heart and soul, inwardness, marrow, meat, pith, sum, nitty-gritty. Examples: "The gist of the prosecutor's argument." "The heart and soul of the republican party." "The nub of the story."