Source : Webster's Revised Unabridged Dictionary (1913)

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

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

Source : WordNet®

nub
     n 1: a small lump or protuberance [syn: {nubble}]
     2: a small piece; "a nub of coal"; "a stub of a pencil" [syn: {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}, {essence}, {gist}, {heart}, {heart and soul}, {inwardness},
         {marrow}, {meat}, {pith}, {sum}, {nitty-gritty}]