Source : Webster's Revised Unabridged Dictionary (1913)

Pith \Pith\, n. [AS. pi?a; akin to D. pit pith, kernel, LG.
   peddik. Cf. {Pit} a kernel.]
   1. (Bot.) The soft spongy substance in the center of the
      stems of many plants and trees, especially those of the
      dicotyledonous or exogenous classes. It consists of
      cellular tissue.

   2.
      (a) (Zo["o]l.) The spongy interior substance of a feather.
      (b) (Anat.) The spinal cord; the marrow.

   3. Hence: The which contains the strength of life; the vital
      or essential part; concentrated force; vigor; strength;
      importance; as, the speech lacked pith.

            Enterprises of great pith and moment. --Shak.

   {Pith paper}. Same as {Rice paper}, under {Rice}.

Pith \Pith\, v. t. (Physiol.)
   To destroy the central nervous system of (an animal, as a
   frog), as by passing a stout wire or needle up and down the
   vertebral canal.

Source : WordNet®

pith
     n 1: soft spongelike central cylinder of the stems of most
          flowering plants
     2: 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}, {nub}, {sum}, {nitty-gritty}]