[1] : The Collaborative International Dictionary of English v.0.48

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.
   1913 webster

[2] : The Collaborative International Dictionary of English v.0.48

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.
      1913 webster

   2.
      a zool. the spongy interior substance of a feather.
      b anat. the spinal cord; the marrow.
          1913 webster

   3. hence: the which contains the strength of life; the vital
      or essential part; concentrated force; vigor; strength;
      importance; as, the speech lacked pith.
      1913 webster

            enterprises of great pith and moment. --shak.
      1913 webster

   pith paper. same as rice paper, under rice.
      1913 webster
see also:
pit pith paper rice paper rice 

[3] : WordNet (r) 2.0

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
see also:
kernel substance core center essence gist 
heart heart and soul inwardness marrow meat 
nub sum nitty-gritty 

[4] : Moby Thesaurus II by Grady Ward, 1.0

204 moby thesaurus words for "pith":
   affective meaning, axiom, axis, backbone, bearing, bench mark,
   bottom, burden, butter, cardinal point, cataplasm, center,
   center of action, center of gravity, centroid, centrum,
   chief thing, chutzpah, climax, coloring, connotation, consequence,
   core, cornerstone, courage, crisis, critical point, crush, crux,
   dead center, denotation, dental pulp, depth, distillate,
   distillation, drift, effect, elixir, epicenter, essence, essential,
   essential matter, essentiality, extension, fabric, flower,
   focal point, focus, force, fulcrum, fundamental, gameness, gist,
   grammatical meaning, gravamen, gravity, great point, grit, guts,
   gutsiness, guttiness, heart, heart of oak, high point, hub,
   hypostasis, idea, impact, implication, import, importance,
   important thing, inner essence, intension, intestinal fortitude,
   issue, kernel, keystone, landmark, lexical meaning,
   literal meaning, magnitude, main point, main thing, marrow, mash,
   material, material point, matter, meaning, meaningfulness, meat,
   medium, medulla, metacenter, mettle, mettlesomeness, middle,
   milestone, moment, momentousness, moxie, mush, nave, navel, nerve,
   nub, nucleus, nuts and bolts, omphalos, overtone, paper pulp,
   paste, pertinence, pivot, plaster, pluck, pluckiness, point,
   porridge, postulate, poultice, practical consequence, principle,
   pudding, pulp, pulp lead, pulpwood, purport, quick, quid, quiddity,
   quintessence, quintessential, rag pulp, range of meaning,
   real issue, real meaning, recap, recapitulation, reference,
   referent, relation, relevance, resume, rock bottom, root,
   run-through, rundown, salient point, sap, sauce, scope,
   semantic cluster, semantic field, sense, short, significance,
   signification, significatum, signifie, sine qua non, smash, soul,
   span of meaning, spirit, sponge, spunk, spunkiness, squash,
   stamina, storm center, stout heart, structural meaning, stuff,
   substance, substantive point, sulfate pulp, sulfite pulp, sum,
   sum and substance, summary, summation, symbolic meaning, tenor,
   the bottom line, the nitty-gritty, the point, thrust,
   totality of associations, toughness, transferred meaning,
   true grit, turning point, umbilicus, unadorned meaning, undertone,
   upshot, value, virtuality, weight, weightiness, white lead,
   wood pulp

Pith >> P Words
Pith, definition of term: Pith
pith_pag1.html

Pith Helmet >> P Words
Pith Helmet, definition of term: Pith Helmet
pith+helmet_pag1.html