From WordNet (r) 3.0 (2006):
nub
n 1: a small lump or protuberance [syn: nub, nubble]
2: a small piece; "a nub of coal"; "a stub of a pencil" [syn:
nub, stub]
3: 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" [syn: kernel, substance, core, center,
centre, essence, gist, heart, heart and soul,
inwardness, marrow, meat, nub, pith, sum, nitty-
gritty]