The Collaborative International Dictionary of English v.0.48:

Kernel \Ker"nel\, n. [OE. kernel, kirnel, curnel, AS. cyrnel,
   fr. corn grain. See Corn, and cf. Kern to harden.]
   1. The essential part of a seed; all that is within the seed
      walls; the edible substance contained in the shell of a
      nut; hence, anything included in a shell, husk, or
      integument; as, the kernel of a nut. See Illust. of
      Endocarp.
      [1913 Webster]

            'A were as good crack a fusty nut with no kernel
                                                  --Shak.
      [1913 Webster]

   2. A single seed or grain; as, a kernel of corn.
      [1913 Webster]

   3. A small mass around which other matter is concreted; a
      nucleus; a concretion or hard lump in the flesh.
      [1913 Webster]

   4. The central, substantial or essential part of anything;
      the gist; the core; as, the kernel of an argument.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Kernel \Ker"nel\, v. i. [imp. & p. p. Kerneledor Kernelled;
   p. pr. & vb. n. Kerneling or Kernelling.]
   To harden or ripen into kernels; to produce kernels. Kerneled

Moby Thesaurus II by Grady Ward, 1.0:

130 Moby Thesaurus words for "kernel":
   Brazil nut, acorn, almond, almond paste, amande, amande douce,
   amandes mondees, axiom, axis, bench mark, berry, bird seed,
   bitter almond, blanched almonds, burnt almond, cardinal point,
   center, center of action, center of gravity, centroid, centrum,
   chief thing, climax, core, cornerstone, crisis, critical point,
   crux, dead center, diameter, diaphragm, distillate, distillation,
   elixir, epicenter, equator, essence, essential, essential matter,
   fabric, flaxseed, flower, focus, fruit, fundamental, gist, goober,
   goober pea, grain, gravamen, great point, ground-pea, groundnut,
   hayseed, heart, high point, hub, hypostasis, important thing,
   inner essence, interior, issue, keystone, landmark, linseed,
   main point, main thing, marrow, material, material point, matter,
   mean, meat, median, medium, medulla, metacenter, middle, midmost,
   midriff, midst, milestone, nave, navel, nigger toe, noisette, noix,
   nub, nubbin, nucleus, nut, nuts and bolts, omphalos, peanut,
   peanut butter, pip, pit, pith, pivot, postulate, principle, quid,
   quiddity, quintessence, real issue, salient point, salted peanuts,
   sap, seed, sine qua non, soul, spirit, stone, storm center, stuff,
   substance, substantive point, sum and substance, sweet almond,
   the bottom line, the nitty-gritty, the point, thick,
   thick of things, turning point, umbilicus, upshot, waist,
   waistline, zone