The Collaborative International Dictionary of English v.0.48:

Nub \Nub\, v. t. [Cf. Knob.]
   To push; to nudge; also, to beckon. [Prov. Eng.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Nub \Nub\, n.
   A jag, or snag; a knob; a protuberance; also, the point or
   gist, as of a story. [Colloq.]
   [1913 Webster]

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]

Moby Thesaurus II by Grady Ward, 1.0:

162 Moby Thesaurus words for "nub":
   axiom, axis, bench mark, bilge, blain, bleb, blister, blob, boss,
   bow, bubble, bulb, bulge, bulla, bump, bunch, burl, button, cahot,
   cardinal point, center, center of action, center of gravity,
   centroid, centrum, chief thing, chine, climax, clump, condyle,
   convex, core, cornerstone, crisis, critical point, crux,
   dead center, distillate, distillation, dowel, ear, elixir,
   epicenter, essence, essential, essential matter, fabric, feel,
   finish, flange, flap, flower, focus, fundamental, gall, gist,
   gnarl, grain, granular texture, gravamen, great point, handle,
   heart, high point, hill, hub, hump, hunch, hypostasis,
   important thing, indentation, inner essence, issue, jog, joggle,
   kernel, keystone, knob, knot, knub, knur, knurl, landmark, lip,
   loop, lump, main point, main thing, marrow, material,
   material point, matter, meat, medium, medulla, metacenter, middle,
   milestone, mole, mountain, nap, nave, navel, nevus, nubbin, nubble,
   nucleus, nuts and bolts, omphalos, papilloma, peg, pile, pit, pith,
   pivot, pock, postulate, principle, protuberance, quid, quiddity,
   quintessence, real issue, rib, ridge, ring, salient point, sap,
   shag, short, shoulder, sine qua non, soul, spine, spirit,
   storm center, structure, stud, stuff, style, substance,
   substantive point, sum and substance, surface, surface texture,
   tab, texture, the bottom line, the nitty-gritty, the point,
   tubercle, tubercule, turning point, umbilicus, upshot, verruca,
   vesicle, wale, wart, weave, welt, woof